Aerosol method and apparatus for making particulate products

ABSTRACT

Provided is an aerosol manufacture facility including an aerosol generator ( 600 ), an aerosol heater ( 604 ), an aerosol cooler ( 604 ), a particle collector ( 606 ), a precursor liquid supply system ( 608 ), a carrier gas supply system ( 610 ), and a cooling gas supply system ( 612 ), and optionally other components. Also provided is an aerosol method for manufacturing particles in the aerosol manufacture facility, which, in one embodiment, involves automated process control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/786,999 which is a United States National Stage under 35 U.S.C § 371of PCT/US99/19163 filed Aug. 23, 1999, which claims priority to U.S.Provisional Patent Application No. 60/098,174 filed Aug. 26, 1998, thecontents of each and every one of which are incorporated herein as ifset forth herein in full.

FIELD OF THE INVENTION

The present invention involves an aerosol manufacture facility,operation of that aerosol manufacture facility, and automated control ofvarious operations involving the aerosol manufacture facility forproducing a particulate product.

BACKGROUND OF THE INVENTION

Powdered materials are used in many manufacturing processes. One largeuse for powders is for thick film deposition to prepare films of avariety of materials. Some thick film applications include, for example,deposition of phosphor materials for flat panel displays, and patterningof electrically conductive features for electronic products.

For thick film applications, and for other applications, there is atrend to use powders of ever smaller particles. Generally desirablefeatures in small particles include a small particle size; a narrowparticle size distribution; a dense, spherical particle morphology; anda crystalline grain structure. Existing technologies for preparingpowdered products, however,often could be improved with respect toattaining all, or substantially all, of these desired features forparticles used in thick film applications.

One method that has been used to make small particles is to precipitatethe particles from a liquid medium. Such liquid precipitation techniquesare often difficult to control to produce particles with the desiredcharacteristics. Also, particles prepared by liquid precipitation routesoften are contaminated with significant quantities of surfactants orother organic materials used during the liquid phase processing.

Aerosol methods have also been used to make a variety of smallparticles. One aerosol method for making small particles is spraypyrolysis, in which an aerosol spray is generated and then converted ina reactor to the desired particles. Spray pyrolysis systems have,however, been mostly experimental, and unsuitable for commercialparticle production. Furthermore, control of particle size distributionis a concern with spray pyrolysis. Also, spray pyrolysis systems areoften inefficient in the use of carrier gases that suspend and carryliquid droplets of the aerosol. Moreover, spray pyrolysis systems arefrequently operated in batch mode, and there is a significant potentialfor inefficiency during transient periods during the early and latestages of particle production. During these periods, variations inparticle properties may degrade the quality of the entire batch.

There is a significant need for improved manufacture techniques formaking powders of small particles for use in thick film and otherapplications.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an aerosol method ofmanufacture suitable for commercial production of particles. Is also anobject to provide an aerosol method to produce a particulate product ata high yield and of a high quality. It is also an object to provide anaerosol method involving significant process control for efficientoperation, especially for batch processing. It is another object of thepresent invention to provide an aerosol method that is at leastpartially automated, to improve efficiency and yield. It is a furtherobject to provide an aerosol manufacture facility in which the aerosolmethod may be conducted. These and other objects of the presentinvention are addressed by the present invention as described herein.

In one aspect, the present invention provides an automated aerosolmethod for processing batches of precursor liquid to manufacture batchesof particles of a selected composition. The method involves automationof at least a portion of the process, with automated features beingcontrolled at the direction of an electronic processor that processesinstructions for manufacture of the particles of the selectedcomposition. The method is often operated in batch mode. In that case,the batch processing begins with batch initiation operations, duringwhich aerosol generation is commenced, proceeds through intermediateoperations, during which the bulk of particle production occurs, andends with batch termination operations, during which aerosol generationis terminated. As used herein, batch mode refers to processing of adiscrete quantity, or batch, of a precursor liquid prepared in a singlepreparation. The batch mode processing of the present invention includesprocessing which might be considered as semi-batch or semi-continuousoperation because of the length of the batch run involved and/or themanner of product removal. Batch mode processing includes, during theintermediate operations, generating, in an aerosol generator, an aerosolstream from carrier gas supplied and precursor liquid supplied to theaerosol generator and processing the aerosol stream through an aerosolheater to form particles of the selected composition. In a preferredembodiment, droplets of the aerosol are produced, in the aerosolgenerator, from a reservoir of circulating precursor liquid thatoverlies a plurality of ultrasonic transducers, which energize precursorliquid in the reservoir to produce the droplets.

In one embodiment of the automated aerosol method of the presentinvention, an operator instructs the electronic processor to directprocessing of a precursor liquid batch to prepare particles of aselected composition. The electronic processor then processesinstructions concerning manufacture of particles of the selectedcomposition and, based on the instructions, the electronic processordirects, during batch initiation operations, automatic control in theaerosol manufacture facility of one or more of commencement of precursorliquid supply to the aerosol generator, commencement of carrier gassupply to the aerosol generator, commencement or increase of heat inputinto the aerosol heater, and activation of ultrasonic transducers in theaerosol generator. During intermediate operations, the electronicprocessor directs automatic control of one or more of carrier gas supplyto the aerosol generator, precursor liquid supply to the aerosolgenerator, and heat input into the aerosol heater. During batchtermination operations, the electronic processor directs automaticcontrol of one or more of deactivation of the ultrasonic transducers,termination of carrier gas supply to the aerosol generator, terminationof precursor liquid supply to the aerosol generator, and reduction ortermination of heat input into the aerosol heater. In a preferredembodiment, all of these noted operations are automatically controlledat the direction of the electronic processor.

The method of the present invention includes significant flexibility toaccommodate automation in a variety of different processing embodiments.For example, the method may include automated cooling of one or moreprocess stream or piece of equipment during the method. In oneembodiment, the aerosol stream, after passing through the aerosolheater, passes to an aerosol cooler where a cooling gas is mixed intothe aerosol stream to lower the temperature of the aerosol stream, topermit subsequent collection of the particles, the supply of the coolinggas to the aerosol cooler being automatically controlled at thedirection of the electronic processor. In one embodiment, the aerosolgenerator includes a pathway for circulation of a cooling liquidadjacent to ultrasonic transducers to cool the ultrasonic transducersduring operation. The cooling liquid pathway is typically interposedbetween the reservoir of precursor liquid and the ultrasonictransducers, so that ultrasonic signals energizing the precursor liquidfirst pass through the cooling liquid. Supply of the cooling liquid isautomated at the direction of the electronic processor. In anotherembodiment, a cooling liquid is supplied to the vicinity of electronicdriver circuits driving the ultrasonic transducers to cool the circuits,with the supply of the cooling liquid being automatically controlled atthe direction of the electronic processor. In another embodiment, acooling liquid is supplied to end caps adjacent entrance and exit endsof the aerosol heater, with supply of the cooling liquid beingautomatically controlled at the direction of the electronic processor.

In one aspect, the present invention addresses a significant problem ofprecursor liquid tending to become more concentrated over time whenaerosol generation is from a recirculating precursor liquid. Theprecursor liquid includes at least one precursor material dissolved orsuspended in a liquid vehicle, typically water. Over time, the precursorliquid tends to become more concentrated in the precursor material. Thisconcentration of the precursor liquid over time can result in anundesirable lack of uniformity in properties of particles that areproduced. The present invention addresses this problem through theaddition of additional liquid vehicle to the aerosol manufacturefacility, during generation of the aerosol stream, in a manner to atleast partially counteract the tendency of the precursor liquid tootherwise become more concentrated. The additional liquid vehicle may beadded, for example, to the aerosol generator, to the liquid supplysystem and/or to the carrier gas supply system.

In one embodiment, the liquid supply system includes two liquidcontainment tanks, or vessels, to facilitate control of the precursorliquid concentration in the liquid supply system and regulation ofsupply of the precursor liquid to the aerosol generator. A first, largervessel acts as the primary supply vessel for the precursor liquid, and asecond, smaller vessel acts as a control vessel. During generation ofthe aerosol stream, precursor liquid is transferred from the firstvessel to the second vessel. Precursor liquid is then supplied to theaerosol generator from the second vessel. Effluent precursor liquid fromthe aerosol generator is returned to the second vessel forrecirculation. Additional liquid vehicle may be added to the secondvessel to at least partially offset the tendency of the precursor liquidto become more concentrated in the precursor material over time.

Furthermore, in one embodiment control of the concentration of theprecursor material in the precursor liquid is automated. For example,the electronic processor may monitor, at some location in the precursorliquid supply system, a property or properties of precursor liquidindicative of the concentration of the precursor material in theprecursor liquid at that location. Based at least in part on themonitored property or properties, the electronic processor then directsautomatic addition, as necessary, of additional precursor liquid to theprecursor liquid supply system to at least partially offset the tendencyof the precursor liquid to become more concentrated over time. Aconvenient location to monitor the property or properties is in thesecond vessel or in the precursor liquid stream being supplied from thesecond vessel to the aerosol generator.

In another aspect, the aerosol manufacture method of the presentinvention addresses detrimental effects on particle quality of transientconditions that may occur during manufacture, and especially duringinitial stages of particle production during batch processing. Theeffects of process transients occurring during the initial stages ofparticle manufacture are, at least in part, addressed with the presentinvention by conditioning equipment of the manufacture facility duringbatch initiation operations, prior to particle manufacture. During theconditioning, the temperature of certain equipment is increased tosimulate conditions that will exist later during steady state particlemanufacture during intermediate operations. The conditioning involvesflowing a carrier gas, prior to particle production, through the aerosolheater at an elevated temperature to simulate temperature and flowconditions that will exist when the aerosol stream is flowing throughthe aerosol heater during steady state particle manufacture. In apreferred embodiment, the heated carrier gas exiting the aerosol heaterthen passes through the aerosol cooler, where it is mixed with coolinggas and conditions the aerosol cooler. Following the aerosol cooler, themixture of cooling gas and carrier gas then flows through the particlecollector to condition the particle collector. With respect to theaerosol generator, conditioning may include, in addition to flow of thecarrier gas, heating the precursor liquid supplied to the aerosolgenerator prior to commencement of aerosol generation. The heating ofthe precursor liquid simulates heating that occurs during aerosolgeneration due to operation of the ultrasonic transducers.

In one aspect, the present invention provides an automated facility foraerosol manufacture of particles according to the method of the presentinvention. The facility includes an aerosol generator, capable ofproducing an aerosol stream from carrier gas and precursor liquid, acarrier gas supply system capable of supplying carrier gas to theaerosol generator, a precursor liquid supply system capable of supplyingprecursor liquid to the aerosol generator, an aerosol heater capable ofheating the aerosol stream to form particles of the desired composition,and an electronic processor capable of processing instructionsconcerning manufacture of particles of the selected composition andcapable of communicating, for the purpose of automated control, with oneor more of the aerosol generator, the carrier gas supply system, theprecursor liquid supply system and the aerosol heater during manufactureof particles in the facility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process block diagram showing one embodiment of the processof the present invention.

FIG. 2 is a side view in cross section of one embodiment of aerosolgenerator of the present invention.

FIG. 3 is a top view of a transducer mounting plate showing a 49transducer array for use in an aerosol generator of the presentinvention.

FIG. 4 is a top view of a transducer mounting plate for a 400 transducerarray for use in an ultrasonic generator of the present invention.

FIG. 5 is a side view of the transducer mounting plate shown in FIG. 4.

FIG. 6 is a partial side view showing the profile of a single transducermounting receptacle of the transducer mounting plate shown in FIG. 4.

FIG. 7 is a partial side view in cross-section showing an alternativeembodiment for mounting an ultrasonic transducer.

FIG. 8 is a top view of a bottom retaining plate for retaining aseparator for use in an aerosol generator of the present invention.

FIG. 9 is a top view of a liquid feed box having a bottom retainingplate to assist in retaining a separator for use in an aerosol generatorof the present invention.

FIG. 10 is a side view of the liquid feed box shown in FIG. 9.

FIG. 11 is a side view of a gas tube for delivering gas within anaerosol generator of the present invention.

FIG. 12 shows a partial top view of gas tubes positioned in a liquidfeed box for distributing gas relative to ultrasonic transducerpositions for use in an aerosol generator of the present invention.

FIG. 13 shows one embodiment for a gas distribution configuration forthe aerosol generator of the present invention.

FIG. 14 shows another embodiment for a gas distribution configurationfor the aerosol generator of the present invention.

FIG. 15 is a top view of one embodiment of a gas distribution plate/gastube assembly of the aerosol generator of the present invention.

FIG. 16 is a side view of one embodiment of the gas distributionplate/gas tube assembly shown in FIG. 15.

FIG. 17 shows one embodiment for orienting a transducer in the aerosolgenerator of the present invention.

FIG. 18 is a top view of a gas manifold for distributing gas within anaerosol generator of the present invention.

FIG. 19 is a side view of the gas manifold shown in FIG. 18.

FIG. 20 is a top view of a generator lid of a hood design for use in anaerosol generator of the present invention.

FIG. 21 is a side view of the generator lid shown in FIG. 20.

FIG. 22 is a process block diagram of one embodiment in the presentinvention including an aerosol concentrator.

FIG. 23 is a process block diagram of one embodiment of the process ofthe present invention including a droplet classifier.

FIG. 24 is a process block diagram of one embodiment of the presentinvention including a particle cooler.

FIG. 25 is a top view of a gas quench cooler of the present invention.

FIG. 26 is an end view of the gas quench cooler shown in FIG. 25.

FIG. 27 is a side view of a perforated conduit of the quench coolershown in FIG. 25.

FIG. 28 is a process block diagram of one embodiment of the presentinvention including a particle coater.

FIG. 29 is a block diagram of one embodiment of the present inventionincluding a particle modifier.

FIGS. 30A-F show cross sections of various particle morphologies of somecomposite particles manufacturable according to the present invention.

FIG. 31 is a schematic showing one embodiment of an aerosol manufacturefacility of the present invention.

FIG. 32 is a schematic showing another embodiment of the aerosolmanufacture facility of the present invention, including cooling of theaerosol generator with a cooling liquid.

FIG. 33 is a flow diagram showing stages of batch processing of thepresent invention.

FIG. 34 is a schematic showing one embodiment of the aerosol manufacturefacility of the present invention, including addition of additionalliquid vehicle to the aerosol generator.

FIG. 35 is a schematic of one embodiment of the aerosol manufacturefacility of the present invention showing the addition of additionalliquid vehicle to the carrier gas supply system.

FIG. 36 is a schematic of one embodiment of the aerosol manufacturefacility of the present invention including the addition of additionalliquid vehicle to the precursor liquid supply system.

FIG. 37 is a schematic of another embodiment of the aerosol manufacturefacility of the present invention, including automated control at thedirection of an electronic processor.

FIG. 38 is a schematic showing one embodiment of the liquid supplysystem of the present invention.

FIG. 39 is a schematic of another embodiment of the precursor liquidsupply system of the present invention.

FIG. 40 is a schematic of another embodiment of the precursor liquidsupply system of the present invention.

FIG. 41 is a schematic of another embodiment of the precursor liquidsupply system of the present invention.

FIG. 42 is a schematic of one embodiment of the carrier gas supplysystem of the present invention.

FIG. 43 is a schematic of one embodiment of the cooling gas supplysystem of the present invention.

FIG. 44 is a schematic showing one embodiment of an aerosol heater ofthe present invention.

FIG. 45 is a simplified cross section of one embodiment of an aerosolheater of the present invention.

FIG. 46 is a schematic showing one embodiment of an aerosol heater ofthe present invention including end caps.

FIG. 47 is a front view of one embodiment of an end cap of the presentinvention.

FIG. 48 is a top view of one embodiment of an end cap of the presentinvention.

FIG. 49 is a schematic showing one embodiment of the aerosol manufacturefacility of the present invention, including automated control of thecooling liquid.

FIG. 50 is a schematic showing one embodiment of a cooling liquid supplysystem of the present invention.

FIG. 51 is a schematic showing one embodiment of the carrier gas supplysystem of the present invention.

FIG. 52 is a schematic of one embodiment of the aerosol manufacturefacility of the present invention, including cooling between the aerosolgenerator and the aerosol heater.

FIG. 53 is a flow diagram showing one embodiment of a sequence of stepsfor the batch initiation operations of the present invention.

FIG. 54 is a flow diagram of one embodiment of a sequence of steps forthe batch initiation operations of the present invention.

FIG. 55 is a flow diagram of one embodiment of a sequence of steps forbatch initiation operations of the present invention.

FIG. 56 is a flow diagram of one embodiment of a sequence of steps forbatch initiation operations of the present invention.

FIG. 57 is a flow diagram of one embodiment of a sequence of steps forbatch initiation operations of the present invention.

FIG. 58 is a flow diagram of one embodiment of a sequence of steps forbatch termination operations of the present invention.

FIG. 59 is a flow diagram of one embodiment of a sequence of steps forbatch termination operations of the present invention.

FIG. 60 is a flow diagram of one embodiment of a sequence of steps forbatch termination operations of the present invention.

FIG. 61 is a schematic of another embodiment of the aerosol manufacturefacility, including an aerosol monitor.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect, the present invention provides a method for preparing aparticulate product. A feed of liquid-containing, flowable medium,including at least one precursor for the desired particulate product, isconverted to aerosol form, with droplets of the medium being dispersedin and suspended by a carrier gas. Liquid from the droplets in theaerosol is then removed to permit formation in a dispersed state of thedesired particles. Typically, the feed precursor is pyrolyzed in afurnace to make the particles. In one embodiment, the particles aresubjected, while still in a dispersed state, to compositional orstructural modification, if desired. Compositional modification mayinclude, for example, coating the particles. Structural modification mayinclude, for example, crystallization, recrystallization ormorphological alteration of the particles. The term powder is often usedherein to refer to the particulate product of the present invention. Theuse of the term powder does not indicate, however, that the particulateproduct must be dry or in any particular environment. Although theparticulate product is typically manufactured in a dry state, theparticulate product may, after manufacture, be placed in a wetenvironment, such as in a slurry.

The process of the present invention is particularly well suited for theproduction of particulate products of finely divided particles having aweight average size, for most applications, in a range having a lowerlimit of about 0.1 micron, preferably about 0.3 micron, more preferablyabout 0.5 micron and most preferably about 0.8 micron; and having anupper limit of about 4 microns, preferably about 3 microns, morepreferably about 2.5 microns and more preferably about 2 microns. Aparticularly preferred range for many applications is a weight averagesize of from about 0.5 micron to about 3 microns, and more particularlyfrom about 0.5 micron to about 2 microns. For some applications,however, other weight average particle sizes may be particularlypreferred.

In addition to making particles within a desired range of weight averageparticle size, with the present invention the particles may be producedwith a desirably narrow size distribution, thereby providing sizeuniformity that is desired for many applications.

In addition to control over particle size and size distribution, themethod of the present invention provides significant flexibility forproducing particles of varying composition, crystallinity andmorphology. For example, the present invention may be used to producehomogeneous particles involving only a single phase or multi-phaseparticles including multiple phases. In the case of multi-phaseparticles, the phases may be present in a variety of morphologies. Forexample, one phase may be uniformly dispersed throughout a matrix ofanother phase. Alternatively, one phase may form an interior core whileanother phase forms a coating that surrounds the core. Othermorphologies are also possible, as discussed more fully below.

Referring now to FIG. 1, one embodiment of the process of the presentinvention is described. A liquid feed 102, including at least oneprecursor for the desired particles, and a carrier gas 104 are fed to anaerosol generator 106 where an aerosol 108 is produced. The aerosol 108is then fed to a furnace 110 where liquid in the aerosol 108 is removedto produce particles 112 that are dispersed in and suspended by gasexiting the furnace 110. The particles 112 are then collected in aparticle collector 114 to produce a particulate product 116.

As used herein, the liquid feed 102 is a feed that includes one or moreflowable liquids as the major constituent(s), such that the feed is aflowable medium. The liquid feed 102 need not comprise only liquidconstituents. The liquid feed 102 may comprise only constituents in oneor more liquid phase, or it may also include particulate materialsuspended in a liquid phase. The liquid feed 102 must, however, becapable of being atomized to form droplets of sufficiently small sizefor preparation of the aerosol 108. Therefore, if the liquid feed 102includes suspended particles, those particles should be relatively smallin relation to the size of droplets in the aerosol 108. Such suspendedparticles should typically be smaller than about 1 micron in size,preferably smaller than about 0.5 micron in size, and more preferablysmaller than about 0.3 micron in size and most preferably smaller thanabout 0.1 micron in size. Most preferably, the suspended particlesshould be able to form a colloid. The suspended particles could befinely divided particles, or could be agglomerate masses comprised ofagglomerated smaller primary particles. For example, 0.5 micronparticles could be agglomerates of nanometer-sized primary particles.When the liquid feed 102 includes suspended particles, the particlestypically comprise no greater than about 25 to 50 weight percent of theliquid feed.

As noted, the liquid feed 102 includes at least one precursor forpreparation of the particles 112. The precursor may be a substance ineither a liquid or solid phase of the liquid feed 102. Frequently, theprecursor will be a material, such as a salt, dissolved in a liquidsolvent of the liquid feed 102. Typical precursor salts include nitrate,chloride, sulfate, acetate and oxalate salts, and the like. Theprecursor may undergo one or more chemical reactions in the furnace 110to assist in production of the particles 112. Alternatively, theprecursor material may contribute to formation of the particles 112without undergoing chemical reaction. This could be the case, forexample, when the liquid feed 102 includes, as a precursor material,suspended particles that are not chemically modified in the furnace 110.In any event, the particles 112 comprise at least one componentoriginally contributed by the precursor.

The liquid feed 102 may include multiple precursor materials, which maybe present together in a single phase or separately in multiple phases.For example, the liquid feed 102 may include multiple precursors insolution in a single liquid vehicle. Alternatively, one precursormaterial could be in a solid particulate phase and a second precursormaterial could be in a liquid phase. Also, one precursor material couldbe in one liquid phase and a second precursor material could be in asecond liquid phase, such as could be the case when the liquid feed 102comprises an emulsion. Different components contributed by differentprecursors may be present in the particles together in a single materialphase, or the different components may be present in different materialphases when the particles 112 are composites of multiple phases.

When the liquid feed 102 includes a soluble precursor, the precursorsolution should be unsaturated to avoid the formation of precipitates.Solutions of salts will typically be used in concentrations in a rangeto provide a solution including from about 1 to about 50 weight percentsolute. Most often, the liquid feed will include a solution with fromabout 5 weight percent to about 40 weight percent solute, and morepreferably to about 30 weight percent solute. Preferably the solvent isaqueous-based for ease of operation, although other solvents, such astoluene or other organic solvents, maybe desirable for specificmaterials. The use of organic solvents, however, can sometimes lead toundesirable carbon contamination in the particles. The pH of theaqueous-based solutions can be adjusted to alter the solubilitycharacteristics of the precursor or precursors in the solution.

The carrier gas 104 may comprise any gaseous medium in which dropletsproduced from the liquid feed 102 may be dispersed in aerosol form.Also, the carrier gas 104 may be inert, in that the carrier gas 104 doesnot participate in formation of the particles 112. Alternatively, thecarrier gas may have one or more active component(s) that contribute toformation of the particles 112. In that regard, the carrier gas mayinclude one or more reactive components that react in the furnace 110 tocontribute to formation of the particles 112.

The aerosol generator 106 atomizes the liquid feed 102 to form dropletsin a manner to permit the carrier gas 104 to sweep the droplets away toform the aerosol 108. The droplets comprise liquid from the liquid feed102. The droplets may, however, also include nonliquid material, such asone or more small particles held in the droplet by the liquid. Forexample, when the particles 112 are composite, or multi-phase,particles, one phase of the composite may be provided in the liquid feed102 in the form of suspended precursor particles and a second phase ofthe composite may be produced in the furnace 110 from one or moreprecursors in the liquid phase of the liquid feed 102. Furthermore theprecursor particles could be included in the liquid feed 102, andtherefore also in droplets of the aerosol 108, for the purpose only ofdispersing the particles for subsequent compositional or structuralmodification during or after processing in the furnace 110.

An important aspect of the present invention is generation of theaerosol 108 with droplets of a small average size, narrow sizedistribution. In this manner, the particles 112 may be produced at adesired small size with a narrow size distribution, which areadvantageous for many applications.

The aerosol generator 106 is capable of producing the aerosol 108 suchthat it includes droplets having a weight average size in a range havinga lower limit of about 1 micron and preferably about 2 microns; and anupper limit of about 10 microns, preferably about 7 microns, morepreferably about 5 microns and most preferably about 4 microns. a weightaverage droplet size in a range of from about 2 microns to about 4microns is more preferred for most applications, with a weight averagedroplet size of about 3 microns being particularly preferred for someapplications. The aerosol generator is also capable of producing theaerosol 108 such that it includes droplets in a narrow sizedistribution. Preferably, the droplets in the aerosol are such that atleast about 70 percent (more preferably at least about 80 weight percentand most preferably at least about 85 weight percent) of the dropletsare smaller than about 10 microns and more preferably at least about 70weight percent (more preferably at least about 80 weight percent andmost preferably at least about 85 weight percent) are smaller than about5 microns. Furthermore, preferably no greater than about 30 weightpercent, more preferably no greater than about 25 weight percent andmost preferably no greater than about 20 weight percent, of the dropletsin the aerosol 108 are larger than about twice the weight averagedroplet size.

Another important aspect of the present invention is that the aerosol108 may be generated without consuming excessive amounts of the carriergas 104. The aerosol generator 106 is capable of producing the aerosol108 such that it has a high loading, or high concentration, of theliquid feed 102 in droplet form. In that regard, the aerosol 108preferably includes greater than about 1×10⁶ droplets per cubiccentimeter of the aerosol 108, more preferably greater than about 5×10⁶droplets per cubic centimeter, still more preferably greater than about1×10⁷ droplets per cubic centimeter, and most preferably greater thanabout 5×10⁷ droplets per cubic centimeter. That the aerosol generator106 can produce such a heavily loaded aerosol 108 is particularlysurprising considering the high quality of the aerosol 108 with respectto small average droplet size and narrow droplet size distribution.Typically, droplet loading in the aerosol is such that the volumetricratio of liquid feed 102 to carrier gas 104 in the aerosol 108 is largerthan about 0.04 milliliters of liquid feed 102 per liter of carrier gas104 in the aerosol 108, preferably larger than about 0.083 millilitersof liquid feed 102 per liter of carrier gas 104 in the aerosol 108, morepreferably larger than about 0.167 milliliters of liquid feed 102 perliter of carrier gas 104, still more preferably larger than about 0.25milliliters of liquid feed 102 per liter of carrier gas 104, and mostpreferably larger than about 0.333 milliliters of liquid feed 102 perliter of carrier gas 104.

This capability of the aerosol generator 106 to produce a heavily loadedaerosol 108 is even more surprising given the high droplet output rateof which the aerosol generator 106 is capable, as discussed more fullybelow. It will be appreciated that the concentration of liquid feed 102in the aerosol 108 will depend upon the specific components andattributes of the liquid feed 102 and, particularly, the size of thedroplets in the aerosol 108. For example, when the average droplet sizeis from about 2 microns to about 4 microns, the droplet loading ispreferably larger than about 0.15 milliliters of aerosol feed 102 perliter of carrier gas 104, more preferably larger than about 0.2milliliters of liquid feed 102 per liter of carrier gas 104, even morepreferably larger than about 0.25 milliliters of liquid feed 102 perliter of carrier gas 104, and most preferably larger than about 0.3milliliters of liquid feed 102 per liter of carrier gas 104. Whenreference is made herein to liters of carrier gas 104, it refers to thevolume that the carrier gas 104 would occupy under conditions ofstandard temperature and pressure.

The furnace 110 may be any suitable device for heating the aerosol 108to evaporate liquid from the droplets of the aerosol 108 and therebypermit formation of the particles 112. For most applications, maximumaverage stream temperatures in the furnace 110 will generally be in arange of from about 500° C. to about 1500° C., and preferably in therange of from about 900° C. to about 1300° C. The maximum average streamtemperature refers to the maximum average temperature that an aerosolstream attains while flowing through the furnace. This is typicallydetermined by a temperature probe inserted into the furnace.

Although longer residence times are possible, for many applications,residence time in the heating zone of the furnace 110 of shorter thanabout 10 seconds is typical. The residence time should be long enough,however, to assure that the particles 112 attain the desired maximumaverage stream temperature for a given heat transfer rate. In thatregard, with extremely short residence times, higher furnacetemperatures could be used to increase the rate of heat transfer so longas the particles 112 attain a maximum temperature within the desiredstream temperature range. That mode of operation, however, is notpreferred. Also, it is noted that as used herein, residence time refersto the actual time for a material to pass through the relevant processequipment. In the case of the furnace, this includes the effect ofincreasing velocity with gas expansion due to heating.

Typically, the furnace 110 will be a tube-shaped furnace, so that theaerosol 108 moving into and through the furnace does not encounter sharpedges on which droplets could collect. Loss of droplets to collection atsharp surfaces results in a lower yield of particles 112. Moreimportant, however, the accumulation of liquid at sharp edges can resultin re-release of undesirably large droplets back into the aerosol 108,which can cause contamination of the particulate product 116 withundesirably large particles. Also, over time, such liquid collection atsharp surfaces can cause fouling of process equipment, impairing processperformance.

The furnace 110 may be any suitable furnace reactor, which typicallyincludes a tubular furnace through which the aerosol flows. Also,although the present invention is described with primary reference to afurnace reactor, which is preferred, it should be recognized that,except as noted, any other thermal reactor, including a flame reactor ora plasma reactor, could be used instead. A furnace reactor is, however,preferred, because of the generally even heating characteristic of afurnace for attaining a uniform stream temperature.

The particle collector 114, may be any suitable apparatus for collectingparticles 112 to produce the particulate product 116. One preferredembodiment of the particle collector 114 uses one or more filter toseparate the particles 112 from gas. Such a filter may be of any type,including a bag filter. Another preferred embodiment of the particlecollector uses one or more cyclone to separate the particles 112. Otherapparatus that may be used in the particle collector 114 includes anelectrostatic precipitator. Also, collection should normally occur at atemperature above the condensation temperature of the gas stream inwhich the particles 112 are suspended. Also, collection should normallybe at a temperature that is low enough to prevent significantagglomeration of the particles 112.

The process and apparatus of the present invention are well-suited forproducing commercial-size batches of extremely high quality particles.In that regard, the process and the accompanying apparatus provideversatility for preparing powder including a wide variety of materials,and easily accommodate shifting of production between differentspecialty batches of particles.

Of significant importance to the operation of the process of the presentinvention is the aerosol generator 106, which must be capable ofproducing a high quality aerosol with high droplet loading, aspreviously noted. With reference to FIG. 2, one embodiment of an aerosolgenerator 106 of the present invention is described. The aerosolgenerator 106 includes a plurality of ultrasonic transducer discs 120that are each mounted in a transducer housing 122. The transducerhousings 122 are mounted to a transducer mounting plate 124, creating anarray of the ultrasonic transducer discs 120. Any convenient spacing maybe used for the ultrasonic transducer discs 120. Center-to-centerspacing of the ultrasonic transducer discs 120 of about 4 centimeters isof ten adequate. The aerosol generator 106, as shown in FIG. 2, includesforty-nine transducers in a 7×7 array. The array configuration is asshown in FIG. 3, which depicts the locations of the transducer housings122 mounted to the transducer mounting plate 124.

With continued reference to FIG. 2, a separator 126, in spaced relationto the transducer discs 120, is retained between a bottom retainingplate 128 and a top retaining plate 130. Gas delivery tubes 132 areconnected to gas distribution manifolds 134, which have gas deliveryports 136. The gas distribution manifolds 134 are housed within agenerator body 138 that is covered by generator lid 140. a transducerdriver 144, having circuitry for driving the transducer discs 120, iselectronically connected with the transducer discs 120 via electricalcables 146.

During operation of the aerosol generator 106, as shown in FIG. 2, thetransducer discs 120 are activated by the transducer driver 144 via theelectrical cables 146. The transducers preferably vibrate at a frequencyof from about 1 MHz to about 5 MHz, more preferably from about 1.5 MHzto about 3 MHz. Frequently used frequencies are at about 1.6 MHz andabout 2.4 MHz. Furthermore, all of the transducer discs 110 should beoperating at substantially the same frequency when an aerosol with anarrow droplet size distribution is desired. This is important becausecommercially available transducers can vary significantly in thickness,sometimes by as much as 10%. It is preferred, however, that thetransducer discs 120 operate at frequencies within a range of 5% aboveand below the median transducer frequency, more preferably within arange of 2.5%, and most preferably within a range of 1%. This can beaccomplished by careful selection of the transducer discs 120 so thatthey all preferably have thicknesses within 5% of the median transducerthickness, more preferably within 2.5%, and most preferably within 1%.

Liquid feed 102 enters through a feed inlet 148 and flows through flowchannels 150 to exit through feed outlet 152. An ultrasonicallytransmissive fluid, typically water, enters through a water inlet 154 tofill a water bath volume 156 and flow through flow channels 158 to exitthrough a water outlet 160. A proper flow rate of the ultrasonicallytransmissive fluid is necessary to cool the transducer discs 120 and toprevent overheating of the ultrasonically transmissive fluid. Ultrasonicsignals from the transducer discs 120 are transmitted, via theultrasonically transmissive fluid, across the water bath volume 156, andultimately across the separator 126, to the liquid feed 102 in flowchannels 150. The ultrasonic signals from the ultrasonic transducerdiscs 120 cause atomization cones 162 to develop in the liquid feed 102at locations corresponding with the transducer discs 120. Carrier gas104 is introduced into the gas delivery tubes 132 and delivered to thevicinity of the atomization cones 162 via gas delivery ports 136. Jetsof carrier gas exit the gas delivery ports 136 in a direction so as toimpinge on the atomization cones 162, thereby sweeping away atomizeddroplets of the liquid feed 102 that are being generated from theatomization cones 162 and creating the aerosol 108, which exits theaerosol generator 106 through an aerosol exit opening 164.

Efficient use of the carrier gas 104 is an important aspect of theaerosol generator 106. The embodiment of the aerosol generator 106 shownin FIG. 2 includes two gas exit ports per atomization cone 162, with thegas ports being positioned above the liquid medium 102 over troughs thatdevelop between the atomization cones 162, such that the exiting carriergas 104 is horizontally directed at the surface of the atomization cones162, thereby efficiently distributing the carrier gas 104 to criticalportions of the liquid feed 102 for effective and efficient sweepingaway of droplets as they form about the ultrasonically energizedatomization cones 162. Furthermore, it is preferred that at least aportion of the opening of each of the gas delivery ports 136, throughwhich the carrier gas exits the gas delivery tubes, should be locatedbelow the top of the atomization cones 162 at which the carrier gas 104is directed. This relative placement of the gas delivery ports 136 isvery important to efficient use of carrier gas 104. Orientation of thegas delivery ports 136 is also important. Preferably, the gas deliveryports 136 are positioned to horizontally direct jets of the carrier gas104 at the atomization cones 162. The aerosol generator 106 permitsgeneration of the aerosol 108 with heavy loading with droplets of thecarrier liquid 102, unlike aerosol generator designs that do notefficiently focus gas delivery to the locations of droplet formation.

Another important feature of the aerosol generator 106, as shown in FIG.2, is the use of the separator 126, which protects the transducer discs120 from direct contact with the liquid feed 102, which is often highlycorrosive. The height of the separator 126 above the top of thetransducer discs 120 should normally be kept as small as possible, andis often in the range of from about 1 centimeter to about 2 centimeters.The top of the liquid feed 102 in the flow channels above the tops ofthe ultrasonic transducer discs 120 is typically in a range of fromabout 2 centimeters to about 5 centimeters, whether or not the aerosolgenerator includes the separator 126, with a distance of about 3 to 4centimeters being preferred. Although the aerosol generator 106 could bemade without the separator 126, in which case the liquid feed 102 wouldbe in direct contact with the transducer discs 120, the highly corrosivenature of the liquid feed 102 can often cause premature failure of thetransducer discs 120. The use of the separator 126, in combination withuse of the ultrasonically transmissive fluid in the water bath volume156 to provide ultrasonic coupling, significantly extending the life ofthe ultrasonic transducers 120. One disadvantage of using the separator126, however, is that the rate of droplet production from theatomization cones 162 is reduced, often by a factor of two or more,relative to designs in which the liquid feed 102 is in direct contactwith the ultrasonic transducer discs 102. Even with the separator 126,however, the aerosol generator 106 used with the present invention iscapable of producing a high quality aerosol with heavy droplet loading,as previously discussed. Suitable materials for the separator 126include, for example, polyamides (such as Kapton™ membranes from DuPont)and other polymer materials, glass, and plexiglass. The mainrequirements for the separator 126 are that it be ultrasonicallytransmissive, corrosion resistant and impermeable.

One alternative to using the separator 126 is to bind acorrosion-resistant protective coating onto the surface of theultrasonic transducer discs 120, thereby preventing the liquid feed 102from contacting the surface of the ultrasonic transducer discs 120. Whenthe ultrasonic transducer discs 120 have a protective coating, theaerosol generator 106 will typically be constructed without the waterbath volume 156 and the liquid feed 102 will flow directly over theultrasonic transducer discs 120. Examples of such protective coatingmaterials include platinum, gold, TEFLON™, epoxies and various plastics.Such coating typically significantly extends transducer life. Also, whenoperating without the separator 126, the aerosol generator 106 willtypically produce the aerosol 108 with a much higher droplet loadingthan when the separator 126 is used.

The design for the aerosol generator 106 based on an array of ultrasonictransducers is versatile and is easily modified to accommodate differentgenerator sizes for different specialty applications. The aerosolgenerator 106 may be designed to include a plurality of ultrasonictransducers in any convenient number. Even for smaller scale production,however, the aerosol generator 106 preferably has at least nineultrasonic transducers, more preferably at least 16 ultrasonictransducers, and even more preferably at least 25 ultrasonictransducers. For larger scale production, however, the aerosol generator106 includes at least 40 ultrasonic transducers, more preferably atleast 100 ultrasonic transducers, and even more preferably at least 400ultrasonic transducers. In some large volume applications, the aerosolgenerator may have at least 1000 ultrasonic transducers.

FIGS. 4-21 show component designs for an aerosol generator 106 includingan array of 400 ultrasonic transducers. Referring first to FIGS. 4 and5, the transducer mounting plate 124 is shown with a design toaccommodate an array of 400 ultrasonic transducers, arranged in foursubarrays of 100 ultrasonic transducers each. The transducer mountingplate 124 has integral vertical walls 172 for containing theultrasonically transmissive fluid, typically water, in a water bathsimilar to the water bath volume 156 described previously with referenceto FIG. 2.

As shown in FIGS. 4 and 5, four hundred transducer mounting receptacles174 are provided in the transducer mounting plate 124 for mountingultrasonic transducers for the desired array. With reference to FIG. 6,the profile of an individual transducer mounting receptacle 174 isshown. A mounting seat 176 accepts an ultrasonic transducer formounting, with a mounted ultrasonic transducer being held in place viascrew holes 178. Opposite the mounting receptacle 176 is a flaredopening 180 through which an ultrasonic signal may be transmitted forthe purpose of generating the aerosol 108, as previously described withreference to FIG. 2.

A preferred transducer mounting configuration, however, is shown in FIG.7 for another configuration for the transducer mounting plate 124. Asseen in FIG. 7, an ultrasonic transducer disc 120 is mounted to thetransducer mounting plate 124 by use of a compression screw 177 threadedinto a threaded receptacle 179. The compression screw 177 bears againstthe ultrasonic transducer disc 120, causing an o-ring 181, situated inan o-ring seat 182 on the transducer mounting plate 124, to becompressed to form a seal between the transducer mounting plate 124 andthe ultrasonic transducer disc 120. This type of transducer mounting isparticularly preferred when the ultrasonic transducer disc 120 includesa protective surface coating, as discussed previously, because the sealof the o-ring to the ultrasonic transducer disc 120 will be inside ofthe outer edge of the protective seal, thereby preventing liquid frompenetrating under the protective surface coating from the edges of theultrasonic transducer disc 120.

Referring now to FIG. 8, the bottom retaining plate 128 for a 400transducer array is shown having a design for mating with the transducermounting plate 124 (shown in FIGS. 4-5). The bottom retaining plate 128has eighty openings 184, arranged in four subgroups 186 of twentyopenings 184 each. Each of the openings 184 corresponds with five of thetransducer mounting receptacles 174 (shown in FIGS. 4 and 5) when thebottom retaining plate 128 is mated with the transducer mounting plate124 to create a volume for a water bath between the transducer mountingplate 124 and the bottom retaining plate 128. The openings 184,therefore, provide a pathway for ultrasonic signals generated byultrasonic transducers to be transmitted through the bottom retainingplate.

Referring now to FIGS. 9 and 10, a liquid feed box 190 for a 400transducer array is shown having the top retaining plate 130 designed tofit over the bottom retaining plate 128 (shown in FIG. 8), with aseparator 126 (not shown) being retained between the bottom retainingplate 128 and the top retaining plate 130 when the aerosol generator 106is assembled. The liquid feed box 190 also includes vertically extendingwalls 192 for containing the liquid feed 102 when the aerosol generatoris in operation. Also shown in FIGS. 9 and 10 is the feed inlet 148 andthe feed outlet 152. An adjustable weir 198 determines the level ofliquid feed 102 in the liquid feed box 190 during operation of theaerosol generator 106.

The top retaining plate 130 of the liquid feed box 190 has eightyopenings 194 therethrough, which are arranged in four subgroups 196 oftwenty openings 194 each. The openings 194 of the top retaining plate130 correspond in size with the openings 184 of the bottom retainingplate 128 (shown in FIG. 8). When the aerosol generator 106 isassembled, the openings 194 through the top retaining plate 130 and theopenings 184 through the bottom retaining plate 128 are aligned, withthe separator 126 positioned therebetween, to permit transmission ofultrasonic signals when the aerosol generator 106 is in operation.

Referring now to FIGS. 9-11, a plurality of gas tube feed-through holes202 extend through the vertically extending walls 192 to either side ofthe assembly including the feed inlet 148 and feed outlet 152 of theliquid feed box 190. The gas tube feed-through holes 202 are designed topermit insertion therethrough of gas tubes 208 of a design as shown inFIG. 11. When the aerosol generator 106 is assembled, a gas tube 208 isinserted through each of the gas tube feed-through holes 202 so that gasdelivery ports 136 in the gas tube 208 will be properly positioned andaligned adjacent the openings 194 in the top retaining plate 130 fordelivery of gas to atomization cones that develop in the liquid feed box190 during operation of the aerosol generator 106. The gas deliveryports 136 are typically holes having a diameter of from about 1.5millimeters to about 3.5 millimeters.

Referring now to FIG. 12, a partial view of the liquid feed box 190 isshown with gas tubes 208A, 208B and 208C positioned adjacent to theopenings 194 through the top retaining plate 130. Also shown in FIG. 12are the relative locations that ultrasonic transducer discs 120 wouldoccupy when the aerosol generator 106 is assembled. As seen in FIG. 12,the gas tube 208A, which is at the edge of the array, has five gasdelivery ports 136. Each of the gas delivery ports 136 is positioned todivert carrier gas 104 to a different one of atomization cones thatdevelop over the array of ultrasonic transducer discs 120 when theaerosol generator 106 is operating. The gas tube 208B, which is one rowin from the edge of the array, is a shorter tube that has ten gasdelivery ports 136, five each on opposing sides of the gas tube 208B.The gas tube 208B, therefore, has gas delivery ports 136 for deliveringgas to atomization cones corresponding with each of ten ultrasonictransducer discs 120. The third gas tube, 208C, is a longer tube thatalso has ten gas delivery ports 136 for delivering gas to atomizationcones corresponding with ten ultrasonic transducer discs 120. The designshown in FIG. 12, therefore, includes one gas delivery port perultrasonic transducer disc 120. Although this is a lower density of gasdelivery ports 136 than for the embodiment of the aerosol generator 106shown in FIG. 2, which includes two gas delivery ports per ultrasonictransducer disc 120, the design shown in FIG. 12 is, nevertheless,capable of producing a dense, high-quality. aerosol without unnecessarywaste of gas.

Referring now to FIG. 13, the flow of carrier gas 104 relative toatomization cones 162 during operation of the aerosol generator 106having a gas distribution configuration to deliver carrier gas 104 fromgas delivery ports on both sides of the gas tubes 208, as was shown forthe gas tubes 208A, 208B and 208C in the gas distribution configurationshown in FIG. 11. The carrier gas 104 sweeps both directions from eachof the gas tubes 208.

An alternative, and preferred, flow for carrier gas 104 is shown in FIG.14. As shown in FIG. 14, carrier gas 104 is delivered from only one sideof each of the gas tubes 208. This results in a sweep of carrier gasfrom all of the gas tubes 208 toward a central area 212. This results ina more uniform flow pattern for aerosol generation that maysignificantly enhance the efficiency with which the carrier gas 104 isused to produce an aerosol. The aerosol that is generated, therefore,tends to be more heavily loaded with liquid droplets.

Another configuration for distributing carrier gas in the aerosolgenerator 106 is shown in FIGS. 15 and 16. In this configuration, thegas tubes 208 are hung from a gas distribution plate 216 adjacent gasflow holes 218 through the gas distribution plate 216. In the aerosolgenerator 106, the gas distribution plate 216 would be mounted above theliquid feed, with the gas flow holes positioned to each correspond withan underlying ultrasonic transducer. Referring specifically to FIG. 16,when the ultrasonic generator 106 is in operation, atomization cones 162develop through the gas flow holes 218, and the gas tubes 208 arelocated such that carrier gas 104 exiting from ports in the gas tubes208 impinge on the atomization cones and flow upward through the gasflow holes. The gas flow holes 218, therefore, act to assist inefficiently distributing the carrier gas 104 about the atomization cones162 for aerosol formation. It should be appreciated that the gasdistribution plates 218 can be made to accommodate any number of the gastubes 208 and gas flow holes 218. For convenience of illustration, theembodiment shown in FIGS. 15 and 16 shows a design having only two ofthe gas tubes 208 and only 16 of the gas flow holes 218. Also, it shouldbe appreciated that the gas distribution plate 216 could be used alone,without the gas tubes 208. In that case, a slight positive pressure ofcarrier gas 104 would be maintained under the gas distribution plate 216and the gas flow holes 218 would be sized to maintain the propervelocity of carrier gas 104 through the gas flow holes 218 for efficientaerosol generation. Because of the relative complexity of operating inthat mode, however, it is not preferred.

Aerosol generation may also be enhanced through mounting of ultrasonictransducers at a slight angle and directing the carrier gas at resultingatomization cones such that the atomization cones are tilting in thesame direction as the direction of flow of carrier gas. Referring toFIG. 17, an ultrasonic transducer disc 120 is shown. The ultrasonictransducer disc 120 is tilted at a tilt angle 114 (typically less than10 degrees), so that the atomization cone 162 will also have a tilt. Itis preferred that the direction of flow of the carrier gas 104 directedat the atomization cone 162 is in the same direction as the tilt of theatomization cone 162.

Referring now to FIGS. 18 and 19, a gas manifold 220 is shown fordistributing gas to the gas tubes 208 in a 400 transducer array design.The gas manifold 220 includes a gas distribution box 222 and pipingstubs 224 for connection with gas tubes 208 (shown in FIG. 11). Insidethe gas distribution box 222 are two gas distribution plates 226 thatform a flow path to assist in distributing the gas equally throughoutthe gas distribution box 222, to promote substantially equal delivery ofgas through the piping stubs 224. The gas manifold 220, as shown inFIGS. 18 and 19, is designed to feed eleven gas tubes 208. For the 400transducer design, a total of four gas manifolds 220 are required.

Referring now to FIGS. 20 and 21, the generator lid 140 is shown for a400 transducer array design. The generator lid 140 mates with and coversthe liquid feed box 190 (shown in FIGS. 9 and 10). The generator lid140, as shown in FIGS. 20 and 21, has a hood design to permit easycollection of the aerosol 108 without subjecting droplets in the aerosol108 to sharp edges on which droplets may coalesce and be lost, andpossibly interfere with the proper operation of the aerosol generator106. When the aerosol generator 106 is in operation, the aerosol 108would be withdrawn via the aerosol exit opening 164 through thegenerator cover 140.

The design and apparatus of the aerosol generator 106 described withreference to FIGS. 2-21, as well as a facility including other processequipment described herein for carrying out the process of the presentinvention for making powders are within the scope of the presentinvention.

Although the aerosol generator 106 produces a high quality aerosol 108having a high droplet loading, it is often desirable to furtherconcentrate the aerosol 108 prior to introduction into the furnace 110.Referring now to FIG. 22, a process flow diagram is shown for oneembodiment of the present invention involving such concentration of theaerosol 108. As shown in FIG. 22, the aerosol 108 from the aerosolgenerator 106 is sent to an aerosol concentrator 236 where excesscarrier gas 238 is withdrawn from the aerosol 108 to produce aconcentrated aerosol 240, which is then fed to the furnace 110.

The aerosol concentrator 236 typically includes one or more virtualimpactors capable of concentrating droplets in the aerosol 108 by afactor of greater than about 2, preferably by a factor of greater thanabout 5, and more preferably by a factor of greater than about 10, toproduce the concentrated aerosol 240. According to the presentinvention, the concentrated aerosol 240 should typically contain greaterthan about 1×10⁷ droplets per cubic centimeter, and more preferably fromabout 5×10⁷ to about 5×10⁸ droplets per cubic centimeter. Aconcentration of about 1×10⁸ droplets per cubic centimeter of theconcentrated aerosol is particularly preferred, because when theconcentrated aerosol 240 is loaded more heavily than that, then thefrequency of collisions between droplets becomes large enough to impairthe properties of the concentrated aerosol 240, resulting in potentialcontamination of the particulate product 116 with an undesirably largequantity of over-sized particles. For example, if the aerosol 108 has aconcentration of about 1×10⁷ droplets per cubic centimeter, and theaerosol concentrator 236 concentrates droplets by a factor of 10, thenthe concentrated aerosol 240 will have a concentration of about 1×10⁸droplets per cubic centimeter. Stated another way, for example, when theaerosol generator generates the aerosol 108 with a droplet loading ofabout 0.167 milliliters liquid feed 102 per liter of carrier gas 104,the concentrated aerosol 240 would be loaded with about 1.67 millilitersof liquid feed 102 per liter of carrier gas 104, assuming the aerosol108 is concentrated by a factor of 10.

Having a high droplet loading in aerosol feed to the furnace 110provides the important advantage of reducing the heating demand on thefurnace 110 and the size of flow conduits required through the furnace.Also, other advantages of having a dense aerosol include a reduction inthe demands on cooling and particle collection components, permittingsignificant equipment and operational savings. Furthermore, as systemcomponents are reduced in size, powder holdup within the system isreduced, which is also desirable. Concentration of the aerosol streamprior to entry into the furnace 110, therefore, provides a substantialadvantage relative to processes that utilize less concentrated aerosolstreams.

The excess carrier gas 238 that is removed in the aerosol concentrator236 typically includes extremely small droplets that are also removedfrom the aerosol 108. Preferably, the droplets removed with the excesscarrier gas 238 have a weight average size of smaller than about 1.5microns, and more preferably smaller than about 1 micron and thedroplets retained in the concentrated aerosol 240 have an averagedroplet size of larger than about 2 microns. For example, a virtualimpactor sized to treat an aerosol stream having a weight averagedroplet size of about three microns might be designed to remove with theexcess carrier gas 238 most droplets smaller than about 1.5 microns insize. Other designs are also possible. When using the aerosol generator106 with the present invention, however, the loss of these very smalldroplets in the aerosol concentrator 236 will typically constitute nomore than about 10 percent by weight, and more preferably no more thanabout 5 percent by weight, of the droplets originally in the aerosolstream that is fed to the concentrator 236. Although the aerosolconcentrator 236 is useful in some situations, it is normally notrequired with the process of the present invention, because the aerosolgenerator 106 is capable, in most circumstances, of generating anaerosol stream that is sufficiently dense. So long as the aerosol streamcoming out of the aerosol generator 102 is sufficiently dense, it ispreferred that the aerosol concentrator not be used. It is a significantadvantage of the present invention that the aerosol generator 106normally generates such a dense aerosol stream that the aerosolconcentrator 236 is not needed. Therefore, the complexity of operationof the aerosol concentrator 236 and accompanying liquid losses maytypically be avoided.

It is important that the aerosol stream (whether it has beenconcentrated or not) that is fed to the furnace 110 have a high dropletflow rate and high droplet loading as would be required for mostindustrial applications. With the present invention, the aerosol streamfed to the furnace preferably includes a droplet flow of greater thanabout 0.5 liters per hour, more preferably greater than about 2 litersper hour, still more preferably greater than about 5 liters per hour,even more preferably greater than about 10 liters per hour, particularlygreater than about 50 liters per hour and most preferably greater thanabout 100 liters per hour; and with the droplet loading being typicallygreater than about 0.04 milliliters of droplets per liter of carriergas, preferably greater than about 0.083 milliliters of droplets perliter of carrier gas 104, more preferably greater than about 0.167milliliters of droplets per liter of carrier gas 104, still morepreferably greater than about 0.25 milliliters of droplets per liter ofcarrier gas 104, particularly greater than about 0.33 milliliters ofdroplets per liter of carrier gas 104 and most preferably greater thanabout 0.83 milliliters of droplets per liter of carrier gas 104.

As discussed previously, the aerosol generator 106 of the presentinvention produces a concentrated, high quality aerosol of micro-sizeddroplets having a relatively narrow size distribution. It has beenfound, however, that for many applications the process of the presentinvention is significantly enhanced by further classifying by size thedroplets in the aerosol 108 prior to introduction of the droplets intothe furnace 110. In this manner, the size and size distribution ofparticles in the particulate product 116 are further controlled.

Referring now to FIG. 23, a process flow diagram is shown for oneembodiment of the process of the present invention including suchdroplet classification. As shown in FIG. 23, the aerosol 108 from theaerosol generator 106 goes to a droplet classifier 280 where oversizeddroplets are removed from the aerosol 108 to prepare a classifiedaerosol 282. Liquid 284 from the oversized droplets that are beingremoved is drained from the droplet classifier 280. This drained liquid284 may advantageously be recycled for use in preparing additionalliquid feed 102.

Any suitable droplet classifier may be used for removing droplets abovea predetermined size. For example, a cyclone could be used to removeover-size droplets. A preferred droplet classifier for manyapplications, however, is an impactor.

In a preferred embodiment of the present invention, the dropletclassifier 280 is typically designed to remove droplets from the aerosol108 that are larger than about 15 microns in size, more preferably toremove droplets larger than about 10 microns in size, even morepreferably to remove droplets of a size larger than about 8 microns insize and most preferably to remove droplets larger than about 5 micronsin size. The droplet classification size in the droplet classifier ispreferably smaller than about 15 microns, more preferably smaller thanabout 10 microns, even more preferably smaller than about 8 microns andmost preferably smaller than about 5 microns. The classification size,also called the classification cut point, is that size at which half ofthe droplets of that size are removed and half of the droplets of thatsize are retained. Because the aerosol generator 106 of the presentinvention initially produces a high quality aerosol 108, having arelatively narrow size distribution of droplets, typically less thanabout 30 weight percent of liquid feed 102 in the aerosol 108 is removedas the drain liquid 284 in the droplet classifier 288, with preferablyless than about 25 weight percent being removed, even more preferablyless than about 20 weight percent being removed and most preferably lessthan about 15 weight percent being removed. Minimizing the removal ofliquid feed 102 from the aerosol 108 is particularly important forcommercial applications to increase the yield of high qualityparticulate product 116. It should be noted, however, that because ofthe superior performance of the aerosol generator 106, it is frequentlynot required to use an impactor or other droplet classifier to obtain adesired absence of oversize droplets to the furnace 110. This is a majoradvantage, because the added complexity and liquid losses accompanyinguse of an impactor may often be avoided with the process of the presentinvention.

Sometimes it is desirable to use both the aerosol concentrator 236 andthe droplet classifier 280 to produce an extremely high quality aerosolstream for introduction into the furnace for the production of particlesof highly controlled size and size distribution. By using both a virtualimpactor and an impactor, both undesirably large and undesirably smalldroplets are removed, thereby producing a classified aerosol with a verynarrow droplet size distribution. Also, the order of the aerosolconcentrator 236 and the aerosol classifier 280 could be with eitherdevice positioned first. Typically, however, the aerosol concentrator236 will be positioned ahead of the droplet classifier 280.

With some applications of the process of the present invention, it maybe possible to collect the particles 112 directly from the output of thefurnace 110. More often, however, it will be desirable to cool theparticles 112 exiting the furnace 110 prior to collection of theparticles 112 in the particle collector 114. Referring now to FIG. 24,one embodiment of the process of the present invention is shown in whichthe particles 112 exiting the furnace 110 are sent to a particle cooler320 to produce a cooled particle stream 322, which is then feed to theparticle collector 114. Although the particle cooler 320 may be anycooling apparatus capable of cooling the particles 112 to the desiredtemperature for introduction into the particle collector 114,traditional heat exchanger designs are not preferred. This is because atraditional heat exchanger design ordinarily directly subjects theaerosol stream, in which the hot particles 112 are suspended, to coolsurfaces. In that situation, significant losses of the particles 112occur due to thermophoretic deposition of the hot particles 112 on thecool surfaces of the heat exchanger. According to the present invention,a gas quench apparatus is provided for use as the particle cooler 320that significantly reduces thermophoretic losses compared to atraditional heat exchanger.

Referring now to FIGS. 25-27, one embodiment of a gas quench cooler 330is shown. The gas quench cooler includes a perforated conduit 332 housedinside of a cooler housing 334 with an annular space 336 located betweenthe cooler housing 334 and the perforated conduit 332. In fluidcommunication with the annular space 336 is a quench gas inlet box 338,inside of which is disposed a portion of an aerosol outlet conduit 340.The perforated conduit 332 extends between the aerosol outlet conduit340 and an aerosol inlet conduit 342. Attached to an opening into thequench gas inlet box 338 are two quench gas feed tubes 344. Referringspecifically to FIG. 27, the perforated tube 332 is shown. Theperforated tube 332 has a plurality of openings 345. The openings 345,when the perforated conduit 332 is assembled into the gas quench cooler330, permit the flow of quench gas 346 from the annular space 336 intothe interior space 348 of the perforated conduit 332. Although theopenings 345 are shown as being round holes, any shape of opening couldbe used, such as slits. Also, the perforated conduit 332 could be aporous screen. Two heat radiation shields 347 prevent downstream radiantheating from the furnace. In most instances, however, it will not benecessary to include the heat radiation shields 347, because downstreamradiant heating from the furnace is normally not a significant problem.Use of the heat radiation shields 347 is not preferred due toparticulate losses that accompany their use.

With continued reference to FIGS. 25-27, operation of the gas quenchcooler 330 will now be described. During operation, the particles 112,carried by and dispersed in a gas stream, enter the gas quench cooler330 through the aerosol inlet conduit 342 and flow into the interiorspace 348 of perforated conduit 332. Quench gas 346 is introducedthrough the quench gas feed tubes 344 into the quench gas inlet box 338.Quench gas 346 entering the quench gas inlet box 338 encounters theouter surface of the aerosol outlet conduit 340, forcing the quench gas346 to flow, in a spiraling, swirling manner, into the annular space336, where the quench gas 346 flows through the openings 345 through thewalls of the perforated conduit 332. Preferably, the gas 346 retainssome swirling motion even after passing into the interior space 348. Inthis way, the particles 112 are quickly cooled with low losses ofparticles to the walls of the gas quench cooler 330. In this manner, thequench gas 346 enters in a radial direction into the interior space 348of the perforated conduit 332 around the entire periphery, orcircumference, of the perforated conduit 332 and over the entire lengthof the perforated conduit 332. The cool quench gas 346 mixes with andcools the hot particles 112, which then exit through the aerosol outletconduit 340 as the cooled particle stream 322. The cooled particlestream 322 can then be sent to the particle collector 114 for particlecollection. The temperature of the cooled particle stream 322 iscontrolled by introducing more or less quench gas. Also, as shown inFIG. 25, the quench gas 346 is fed into the quench cooler 330 in counterflow to flow of the particles. Alternatively, the quench cooler could bedesigned so that the quench gas 346 is fed into the quench cooler inconcurrent flow with the flow of the particles 112. The amount of quenchgas 346 fed to the gas quench cooler 330 will depend upon the specificmaterial being made and the specific operating conditions. The quantityof quench gas 346 used, however, must be sufficient to reduce thetemperature of the aerosol steam including the particles 112 to thedesired temperature. Typically, the particles 112 are cooled to atemperature at least below about 200° C., and often lower. The onlylimitation on how much the particles 112 are cooled is that the cooledparticle stream 322 must be at a temperature that is above thecondensation temperature for water as another condensible vapor in thestream. The temperature of the cooled particle stream 322 is often at atemperature of from about 50° C. to about 120° C.

Because of the entry of quench gas 346 into the interior space 348 ofthe perforated conduit 322 in a radial direction about the entirecircumference and length of the perforated conduit 322, a buffer of thecool quench gas 346 is formed about the inner wall of the perforatedconduit 332, thereby significantly inhibiting the loss of hot particles112 due to thermophoretic deposition on the cool wall of the perforatedconduit 332. In operation, the quench gas 346 exiting the openings 345and entering into the interior space 348 should have a radial velocity(velocity inward toward the center of the circular cross-section of theperforated conduit 332) of larger than the thermophoretic velocity ofthe particles 112 inside the perforated conduit 332 in a directionradially outward toward the perforated wall of the perforated conduit332.

As seen in FIGS. 25-27, the gas quench cooler 330 includes a flow pathfor the particles 112 through the gas quench cooler of a substantiallyconstant cross-sectional shape and area. Preferably, the flow paththrough the gas quench cooler 330 will have the same cross-sectionalshape and area as the flow path through the furnace 110 and through theconduit delivering the aerosol 108 from the aerosol generator 106 to thefurnace 110.

Also, particle cooling in the quench cooler is accomplished veryquickly, reducing the potential for thermophoretic losses duringcooling. The total residence time for the aerosol flowing through boththe heated zone of the furnace 110 and through the quench cooler istypically shorter than about 5 seconds, more preferably shorter thanabout 2 seconds, and most preferably shorter than about 1 second.

In an additional embodiment, the process of the present invention canalso incorporate compositional modification of the particles 112 exitingthe furnace. Most commonly, the compositional modification will involveforming on the particles 112 a material phase that is different thanthat of the particles 112, such as by coating the particles 112 with acoating material. One embodiment of the process of the present inventionincorporating particle coating is shown in FIG. 28. As shown in FIG. 28,the particles 112 exiting from the furnace 110 go to a particle coater350 where a coating is placed over the outer surface of the particles112 to form coated particles 352, which are then sent to the particlecollector 114 for preparation of the particulate product 116.

In the particle coater 350, the particles 112 are coated using anysuitable particle coating technology, such as by gas-to-particleconversion. Preferably, however, the coating is accomplished by chemicalvapor deposition (CVD) and/or physical vapor deposition (PVD). In CVDcoating, one or more vapor phase coating precursors are reacted to forma surface coating on the particles 112. Preferred coatings deposited byCVD include oxides, such as silica, alumina, titania and zirconia, andelemental metals. For example, silica may be deposited using a silaneprecursor, such as tetrachlorosilane. In PVD coating, coating materialphysically deposits on the surface of the particles 112. Preferredcoatings deposited by PVD include organic materials and elementalmetals, such as elemental silver, copper and gold. Another possiblesurface coating method is surface conversion of the surface portion ofthe particles 112 by reaction with a vapor phase reactant to convert asurface portion of the particles to a different material than thatoriginally contained in the particles 112. Although any suitableapparatus may be used for the particle coater 350, when a gaseouscoating feed involving coating precursors is used, such as for CVD andPVD, feed of the gaseous coating feed is introduced through acircumferentially perforated conduit, such as was described for thequench cooler 330 with reference to FIGS. 25-27. In some instances, thequench cooler 330 may also act as the particle coater 350, when coatingmaterial precursors are included in the quench gas 346.

With continued reference primarily to FIG. 28, in a preferredembodiment, when the particles 112 are coated according to the processof the present invention, the particles 112 are also manufactured viathe aerosol process of the present invention, as previously described.The process of the present invention can, however, be used to coatparticles that have been premanufactured by a different process, such asby a liquid precipitation route. When coating particles that have beenpremanufactured by a different route, such as by liquid precipitation,it is preferred that the particles remain in a dispersed state from thetime of manufacture to the time that the particles are introduced inslurry form into the aerosol generator 106 for preparation of theaerosol 108 to form the dry particles 112 in the furnace 110, whichparticles 112 can then be coated in the particle coater 350. Maintainingparticles in a dispersed state from manufacture through coating avoidsproblems associated with agglomeration and redispersion of particles ifparticles must be redispersed in the liquid feed 102 for feed to theaerosol generator 106. For example, for particles originallyprecipitated from a liquid medium, the liquid medium containing thesuspended precipitated particles could be used to form the liquid feed102 to the aerosol generator 106. It should be noted that the particlecoater 350 could be an integral extension of the furnace 110 or could bea separate piece of equipment.

In a further embodiment of the present invention, following preparationof the particles 112 in the furnace 110, the particles 112 may then bestructurally modified to impart desired physical properties prior toparticle collection. Referring now to FIG. 29, one embodiment of theprocess of the present invention is shown including such structuralparticle modification. The particles 112 exiting the furnace 110 go to aparticle modifier 360 where the particles are structurally modified toform modified particles 362, which are then sent to the particlecollector 114 for preparation of the particulate product 116. Theparticle modifier 360 is typically a furnace, such as an annealingfurnace, which may be integral with the furnace 110 or may be a separateheating device. Regardless, it is important that the particle modifier360 have temperature control that is independent of the furnace 110, sothat the proper conditions for particle modification may be providedseparate from conditions required of the furnace 110 to prepare theparticles 112. The particle modifier 360, therefore, typically providesa temperature controlled environment and necessary residence time toeffect the desired structural modification of the particles 112.

The structural modification that occurs in the particle modifier 360 maybe any modification to the crystalline structure or morphology of theparticles 112. For example, the particles 112 may be annealed in theparticle modifier 360 to density the particles 112 or to recrystallizethe particles 112 into a polycrystalline or single crystalline form.Also, especially in the case of composite particles 112, the particlesmay be annealed for a sufficient time to permit redistribution withinthe particles 112 of different material phases.

The initial morphology of composite particles made in the furnace 110,according to the present invention, could take a variety of forms,depending upon the specified materials involved and the specificprocessing conditions. Examples of some possible composite particlemorphologies, manufacturable according to the present invention areshown in FIGS. 30A-F. These morphologies could be of the particles asinitially produced in the furnace 110 or that result from structuralmodification in the particle modifier 360. Furthermore, the compositeparticles could include a mixture of the morphological attributes shownin FIG. 30.

When making multi-phase particles, a preferred multi-phase particleincludes a metallic phase, such as with at least one of palladium,silver, nickel and copper, and a nonmetallic phase. Preferred for thenonmetallic phase is at least one of silica, alumina, titania andzirconia. Another preferred nonmetallic phase includes a titanate, andpreferably a titanate of at least one of barium, strontium, neodymium,calcium, magnesium and lead.

Aerosol generation with the process of the present invention has thusfar been described with respect to the ultrasonic aerosol generator. Useof the ultrasonic generator is preferred for the process of the presentinvention because of the extremely high quality and dense aerosolgenerated. In some instances, however, the aerosol generator for theprocess of the present invention may have a different design dependingupon the specific application. For example, when larger particles aredesired, such as those having a weight average size of larger than about3 microns, a spray nozzle atomizer may be preferred. Forsmaller-particle applications, however, and particularly for thoseapplications to produce particles smaller than about 3 microns, andpreferably smaller than about 2 microns in size, as is generally desiredwith the particles of the present invention, the ultrasonic generator,as described herein, is particularly preferred. In that regard, theultrasonic generator of the present invention is particularly preferredfor when making particles with a weight average size of from about 0.2micron to about 3 microns.

Although ultrasonic aerosol generators have been used for medicalapplications and home humidifiers, use of ultrasonic generators forspray pyrolysis particle manufacture has largely been confined tosmall-scale, experimental situations. The ultrasonic aerosol generatorof the present invention described with reference to FIGS. 2-21,however, is well suited for commercial production of high qualitypowders with a small average size and a narrow size distribution. Inthat regard, the aerosol generator produces a high quality aerosol, withheavy droplet loading and at a high rate of production. Such acombination of small droplet size, narrow size distribution, heavydroplet loading, and high production rate provide significant advantagesover existing aerosol generators that usually suffer from at least oneof inadequately narrow size distribution, undesirably low dropletloading, or unacceptably low production rate.

Through the careful and controlled design of the ultrasonic generator ofthe present invention, an aerosol may be produced typically havinggreater than about 70 weight percent (and preferably greater than about80 weight percent) of droplets in the size range of from about 1 micronto about 10 microns, preferably in a size range of from about 1 micronto about 5 microns and more preferably from about 2 microns to about 4microns. Also, the ultrasonic generator of the present invention iscapable of delivering high output rates of liquid feed in the aerosol.The rate of liquid feed, at the high liquid loadings previouslydescribed, is preferably greater than about 25 milliliters per hour pertransducer, more preferably greater than about 37.5 milliliters per hourper transducer, even more preferably greater than about 50 millilitersper hour per transducer and most preferably greater than about 100millimeters per hour per transducer. This high level of performance isdesirable for commercial operations and is accomplished with the presentinvention with a relatively simple design including a single precursorbath over an array of ultrasonic transducers. The ultrasonic generatoris made for high aerosol production rates at a high droplet loading, andwith a narrow size distribution of droplets. The generator preferablyproduces an aerosol at a rate of greater than about 0.5 liter per hourof droplets, more preferably greater than about 2 liters per hour ofdroplets, still more preferably greater than about 5 liters per hour ofdroplets, even more preferably greater than about 10 liters per hour ofdroplets and most preferably greater than about 40 liters per hour ofdroplets. For example, when the aerosol generator has a 400 transducerdesign, as described with reference to FIGS. 3-21, the aerosol generatoris capable of producing a high quality aerosol having high dropletloading as previously described, at a total production rate ofpreferably greater than about 10 liters per hour of liquid feed, morepreferably greater than about 15 liters per hour of liquid feed, evenmore preferably greater than about 20 liters per hour of liquid feed andmost preferably greater than about 40 liters per hour of liquid feed.

Under most operating conditions, when using such an aerosol generator,total particulate product produced is preferably greater than about 0.5gram per hour per transducer, more preferably greater than about 0.75gram per hour per transducer, even more preferably greater than about1.0 gram per hour per transducer and most preferably greater than about2.0 grams per hour per transducer.

The concentrations of soluble precursors in the liquid feed 102 willvary depending upon the particular materials involved and the particularparticle composition and particle morphology desired. For mostapplications, when soluble precursor(s) are used, the solubleprecursor(s) are present at a concentration of from about 1-50 weightpercent of the liquid feed. 102. In any event, however, when solubleprecursors are used, the precursors should be at a low enoughconcentration to permit the liquid feed to be ultrasonically atomizedand to prevent premature precipitation of materials from the liquid feed102. The concentration of suspended particulate precursors will alsovary depending upon the particular materials involved in the particularapplication.

Powders of a variety of materials may be made according to the presentinvention, with the powders so produced being an important aspect of theinvention. The particles may include, for example, single phase ormulti-phase particles. Also, the particles may include a metallic phaseor a nonmetallic phase.

With the present invention, these various powders may be made with verydesirable attributes for a variety of applications. In that regard, thepowders are typically made with a small weight average particle size,narrow particle size distribution, spheroidal particle shape, and highdensity relative to a theoretical density for the material of theparticles. Also, the particles of the powder typically are eithersubstantially single crystalline or are polycrystalline and with a largemean crystallite size.

With respect to particle size, the powders are characterized generallyas having a weight average particle size that typically is in the rangeof from about 0.05 micron to about 4 microns, with most powders having aweight average size of from about 0.1 micron to about 3 microns. Withthe process of the present invention, however, particle size maygenerally be controlled to provide particles with a desired size.Particle size is varied primarily by altering the frequency ofultrasonic transducers in the aerosol generator and by altering theconcentration of precursors in the liquid feed. Lower ultrasonicfrequencies tend to produce larger particles, while higher frequenciestend to produce smaller particles. Also, higher precursor concentrationsin the liquid feed tend to produce larger particles and lower precursorconcentrations in the liquid feed tend to produce smaller particles.

The particles are typically characterized as having a weight averageparticle size in a range having a lower limit, depending upon theapplication, of from about 0.1 micron, or about 0.2 micron, or about 0.3micron, or about 0.5 micron, or about 0.8 micron, or about 1 micron; andhaving an upper limit, depending upon the application, of about 4microns, or about 3 microns, or about 2.5 microns, or about 2 microns,or about 1 micron, or about 0.8 micron, or about 0.6 micron. Powdershaving a weight average size range defined by any combination of one ofthe specified upper limits and one of the specified lower limits arewithin the scope of the present invention, so long as the upper limit islarger than the lower limit.

As will be appreciated by those skilled in the art, the size ofparticles as referred to herein is the size of what is often referred toas the primary particles. As is known in the art, it is common forparticles manufactured by an aerosol route to form loosely bound, or“soft,” agglomerates when the particles are collected. These softagglomerates are easily dispersed back to the loose primary particles,such as by sonication, sieving or low shear milling. A preferred methodfor determining particle size is to first disperse the particles in aliquid medium, such as water, by sonication in an ultrasonic bath orhorn to disperse soft agglomerates that may have formed, and to thendetermine primary particle size attributes by light scattering, such asin a Microtrac™ or other analytical equipment.

The powders are also characterized as having a narrow particle sizedistribution, typically with greater than about 75 weight percent,preferably greater than about 90 weight percent, and more preferablygreater than about 95 weight percent of the particles in the powderhaving a size of smaller than two times the weight average particlesize, and even more particularly smaller than about 1.5 times the weightaverage particle size.

The powders are also typically characterized as being comprised ofspheroidal particles. In that regard, the particles are substantiallyspherical, in that the particles are not jagged or irregular in shape,although the particles may become faceted as the crystallite size in theparticles increases. Spheroidal particles are advantageous because theytypically have increased dispersibility and flowability in pasteformulations relative to jagged or irregular particles.

Although in some instances the powders may be made as very porous orhollow particles, the powders are usually characterized as being verydense, with the particles typically having a density of at least about80%, preferably at least about 90% and more preferably at least about95%, of a theoretical density. The theoretical density is that densitythat particles would have assuming that the particles included zeroporosity. As used herein, the density of a particle is as measured byhelium pycnometry. High particle density is particularly advantageousfor thick film applications involving a fired film, because higherdensity particles tend to exhibit reduced shrinkage during sinteringthan highly porous particles.

The powders are further characterized as typically having a high degreeof purity, with generally no more than about 0.1 atomic percentimpurities and preferably no more than about 0.01 atomic percentimpurities. One significant characteristic of the powders of the presentinvention is that they may be made to be substantially free of organicmaterials, if desired, and particularly to be substantially free ofsurfactants. This is a significant advantage over particles made by aliquid route, which typically include residual surfactants. Theseresidual surfactants can significantly impair the utility of theparticles, especially in making thick film pastes.

Efficient manufacture of particulate product through the aerosolmanufacture method of the present invention requires control of a numberof flow streams and heat input. FIG. 31 shows a schematic of an aerosolmanufacture facility of the present invention showing major components.

The aerosol manufacture facility, as shown in FIG. 31, includes anaerosol generator 600, an aerosol heater 602 in fluid communication withthe aerosol generator 600, an aerosol cooler 604 in fluid communicationwith the aerosol heater 602, and a particle collector 606 in fluidcommunication with the aerosol cooler 604. The aerosol manufacturefacility also includes a precursor liquid supply system 608, a carriergas supply system 610 and a cooling gas supply system 612.

During operation of the aerosol manufacture facility to produce aparticulate product, precursor liquid is circulated to the aerosolgenerator 600 from the precursor liquid supply system 608. Circulationof the precursor liquid includes supplying a precursor liquid feed 620from the precursor liquid supply system 608 to the aerosol generator 600and removing a precursor liquid effluent 622 from the aerosol generator600 and returning the precursor liquid effluent 622 to the precursorliquid supply system 608, for recirculation to the aerosol generator 600as part of the precursor liquid feed 620. Carrier gas 624 is supplied tothe aerosol generator 600 from the carrier gas supply system 610. In theaerosol generator 600, there is a reservoir of the precursor liquidoverlying ultrasonic transducers, as previously described with referenceto FIGS. 2-21. When the ultrasonic transducers in the aerosol generatorare activated, droplets of the precursor liquid are formed. Thesedroplets combine with and are carried away by the carrier gas 624 in theform of an aerosol stream which exits the aerosol generator 600 andpasses through a conduit 614 to the aerosol heater 602, where particlesare formed in the aerosol stream. Formation of the particles involvesheating the aerosol stream to vaporize the liquid vehicle from thedroplets. The aerosol stream, now including particles as a dispersephase, exits the aerosol heater 602 through a conduit 616 and passes tothe aerosol cooler 604. In the aerosol cooler 604, the aerosol stream ismixed with a cooling gas 624 supplied to the aerosol cooler 604 from thecooling gas supply system 612, to lower the temperature of the aerosolstream to cool the particles. The aerosol stream exits the aerosolcooler 604 through the conduit 618 and passes to the particle collector606. In the particle collector 606, the particles are removed from theaerosol stream. The aerosol generator 600, aerosol heater 602, aerosolcooler 604 and particle collector 606 may comprise any suitableequipment, such as has been previously described. In that regard, theaerosol generator 600 is typically an ultrasonic aerosol generator of adesign as previously described; the aerosol heater 602 is typically afurnace, such as tube furnace; the aerosol cooler is typically aquench-style cooler, such as previously described; and the particlecollector typically comprises a filter, a cyclone separator or anelectrostatic precipitator.

As can be seen in FIG. 31, a number of process flows must be coordinatedto efficiently produce particles in the aerosol manufacture facility.Many variations to the aerosol manufacture facility are possible,several of which could involve even more complex operations than thatshown in FIG. 31. For example, FIG. 32 is a schematic showing anotherembodiment of the aerosol manufacture facility. As shown in FIG. 32, theaerosol manufacture facility includes, in addition to the features shownin FIG. 31, a cooling liquid supply system 630. Operation of the aerosolmanufacture facility to make particles involves a cooling liquid feed632, typically water, supplied to the aerosol generator 600 from thecooling liquid supply system 630. A cooling liquid effluent 634 isreturned from the aerosol generator 600 to the cooling liquid supplysystem 630. The cooling liquid supply system 630 would be used, forexample, when the aerosol generator 600 is of a design incorporatingcooling of the ultrasonic transducers during operation, as previouslydiscussed with respect to aerosol generator designs. Also, oralternatively, the cooling liquid supply system 630 could be used tocool driver circuitry that drives the ultrasonic transducers to preventcircuit overheating.

Manufacture of particles in the aerosol manufacture facility may occurin a batch mode or a continuous mode of operation. In most instances,however, the aerosol manufacture facility will be operated in a batchmode. As used herein, unless otherwise noted, operating in a batch moderefers to processing of a batch of precursor liquid to produceparticles, and includes processing that could be considered as beingtechnically semi-batch or semi-continuous in nature. A batch ofprecursor liquid refers to a discrete volume of precursor liquid to beprocessed. The particles produced from processing of a batch ofprecursor liquid are generally referred to as a batch of particles or apowder batch, even though the particles may be removed from the systemperiodically at different times during processing of the precursorliquid batch. When operated in a batch mode, the aerosol manufacturefacility may be designed with appropriately sized equipment toaccommodate any desired precursor liquid batch size. In some instances,when processing large precursor liquid batches, processing of theprecursor liquid batch in batch mode may require a batch run time of aweek or more.

Referring now to FIG. 33, a flow diagram is shown for processing a batchof precursor liquid in the aerosol manufacture facility operated inbatch mode. As seen in FIG. 33, the processing of a batch proceedsthrough three stages of operation, namely batch initiation operations,intermediate operations, and batch termination operations. In a firststage, the batch initiation operations involve preliminary operations toprepare the system for generation of and processing of the aerosolstream. The batch initiation operations, generally include initiatingflows, such as of carrier gas, precursor liquid and cooling gas, andconditioning equipment, such as the furnace, the aerosol generator, theaerosol cooler and the particle collector, all prior to commencinggeneration of the aerosol stream in the aerosol generator. Typically,the final step in the batch initiation operations is to commencegeneration of the aerosol stream. This is usually accomplished byactivating the ultrasonic transducers once initial preparations arecomplete.

In a second stage, the intermediate operations involve manufacture ofparticles after the commencement of generation of the aerosol stream.Referring briefly to FIG. 31, the intermediate operations generallyinclude generating the aerosol stream in the aerosol generator 600, andthen flowing the aerosol stream to the aerosol heater 602, where theaerosol stream is heated and the particles are formed. The aerosolstream, containing the particles, then passes to the aerosol cooler 604,where the cooling gas 624 is mixed with the aerosol stream to reduce thetemperature of the aerosol stream. The aerosol stream then passes to theparticle collector 606 where the particles are removed from the aerosolstream. The intermediate operations may last for a week, or more, forlarge precursor liquid batches and typically include particlemanufacture in a steady state or quasi-steady state operation. In thisrespect, the intermediate operations are analogous to operating in acontinuous mode, and the discussions herein relating to the intermediateoperations apply equally to operation of the aerosol manufacturefacility in a continuous mode of operation. Furthermore, although theintermediate operations typically involve steady state or quasi-steadystate processing, the steady state or quasi-steady state condition maybe periodically interrupted to permit routine maintenance, to permitremoval of accumulated particles from the particle collector 606 or forother reasons. Such interruptions preferably occur no more frequentlythan about once per day, and preferably for no longer than a few hoursfor each occurrence.

Referring again to FIG. 33, in a third stage of batch processing, thebatch termination operations generally involve terminating particlemanufacture and shutting down process flows and equipment. For example,the batch termination operations typically include deactivating theultrasonic transducers to cease generation of the aerosol stream,purging remaining aerosol from the system, and terminating the flows ofcarrier gas, precursor liquid and cooling gas.

As noted, the intermediate operations are generally analogous tooperations in a continuous mode. Likewise, the batch initiationoperations are analogous to start-up operations that may precedecontinuous mode operation. Also, the batch termination operations areanalogous to a periodic shut-down that may be required even when theaerosol manufacture facility is operated in a continuous mode.Therefore, the discussions herein, although focused primarily on batchmode of operation, apply equally to a continuous mode of operation.

Efficient control of the batch initiation operations, the intermediateoperations, the batch termination operations, and transitions betweenthese stages is an important aspect of the present invention forefficient operation of the aerosol manufacture facility.

One major aspect of the present invention is control of theconcentration of the precursor material in the precursor liquid beingprocessed in a batch, especially during the intermediate operations.This is important because, over time, the circulating precursor liquidhas a tendency to become more concentrated in the precursor material.Referring to FIGS. 31 and 33, during the intermediate operations, theprecursor liquid feed 620 is divided, in the aerosol generator, into atleast two portions. A first portion exits the aerosol generator in thedroplets of the aerosol stream. A second portion exits the aerosol asthe precursor liquid effluent 622 that is returned to the precursorliquid supply system for recirculation.

The problem with concentration of the precursor material over timeresults primarily from vaporization, in the aerosol generator 600, ofsome of the liquid vehicle from the precursor liquid circulating throughthe aerosol generator 600. The tendency of the circulating precursorliquid to become more concentrated in the precursor material can be aserious problem when it is desired to make a uniform batch of particles,as is usually the case. This significant problem is addressed with thepresent invention through the addition of additional liquid vehicle tothe aerosol manufacture facility during generation of the aerosol streamto at least partially offset the tendency of the precursor liquid tootherwise become more concentrated in the precursor material. Theadditional liquid vehicle may be added at any convenient location withinthe aerosol manufacture facility to effect the desired concentration.Preferred locations for adding the additional liquid vehicle include theaerosol generator 600, the carrier gas supply system 610, and theprecursor liquid supply system 608. FIG. 34 shows a schematic of oneembodiment of the aerosol manufacture facility including the addition ofadditional liquid vehicle 636 directly to the aerosol generator 600.FIG. 35 shows one embodiment of the aerosol manufacture facilityincluding the addition of the additional liquid vehicle 636 to thecarrier gas supply system 610. FIG. 36 shows one embodiment of theaerosol manufacture facility including addition of the additional liquidvehicle 636 to the precursor liquid supply system 608. With the presentinvention, the concentration of the precursor material in the precursorliquid feed 620 typically varies by no more than about 20 percentrelative to the maximum concentration experienced in the precursorliquid feed, and preferably varies by no more than about 10 percent andmore preferably by no more than about 5 percent.

In addition to becoming more concentrated in the precursor material, itis possible also that the precursor liquid may become concentrated in ordepleted in some other component, for which appropriate processadjustments may be made. For example, when making some materials, theprecursor liquid comprises an acidic aqueous nitrate solution. In thatsituation, significant nitric acid can be lost to volatilization in theaerosol generator and the precursor liquid will, therefore, becomedepleted in nitric acid over time. Additional nitric acid may, however,be added, to at least partially offset the depletion. The additionalnitric acid could be added together with the additional liquid vehicle636, as an aqueous solution of nitric acid, or could be addedseparately.

Another significant aspect of the present invention concerning efficientcontrol and operation of batch processing in the aerosol manufacturefacility is that the processing may, at least in part, be automated,with automated control of at least a portion of one of the batchinitiation operations, the intermediate operations and the batchtermination operations. In preferred process embodiments, all three ofthe stages of batch processing are significantly automated. In onepreferred automated mode of operation, an operator directs an electronicprocessor to process a batch of precursor liquid to prepare a batch ofparticles of a selected composition. The processor then processesinstructions concerning manufacture of particles of the selectedcomposition and automatically directs the aerosol manufacture facilityto manufacture a batch of particles of the selected composition.

Referring now to FIG. 37, a schematic of one embodiment of the aerosolmanufacture facility is shown in which an electronic processor is usedto direct control of batch processing of the aerosol manufacturefacility. As shown in FIG. 37, an electronic processor 640 communicateswith an electronic controller 642, which communicates with the precursorliquid supply system 608, the carrier gas supply system 610, the coolinggas supply system 612, the aerosol heater 602 and the aerosol generator600. During operation, the electronic processor 640 communicatesdirections to the controller 642, which transmits control signals toeffectuate automatic actuation of actuatable equipment, such asactuatable flow control valves, pumps, heating elements, etc. Theelectronic processor 640 also monitors selected conditions, via thecontroller 642, in the aerosol manufacture facility. Monitoredconditions may include conditions such as properties of the precursorliquid, temperatures, pressures, flow rates, liquid levels, etc. Basedat least on one of these monitored conditions, the electronic processor640 reevaluates control requirements and directs a change of controlledparameters, as required.

It will be appreciated that the electronic processor 640 is ultimatelyresponsible for directing the process control, even though the actualcontrol signals to effectuate the control come from the controller 642.The controller 642 merely facilitates communication between theelectronic processor 640 and actuatable equipment through which processcontrol is effectuated. For example, the controller 642 is capable ofconverting analog signals received from process equipment into digitalsignals to send to the electronic processor 640 for processing. Also,the controller 642 is capable of converting digital signals receivedfrom the electronic processor to analog control signals to send toactuatable equipment. The controller 642 is also capable of relaying asignal without conversion. The controller 642 may comprise a single unitor may comprise a plurality of components that are coordinated tofacilitate communication between the electronic processor 640 anddifferent portions of the aerosol manufacture facility. Moreover, theactuatable equipment may be actuated electronically or pneumatically. Aswill be appreciated, the use of pneumatically actuated equipment mayrequire transducers to convert electronic signals from the controller642 into pneumatic signals to actuate the equipment.

The electronic processor 640 may be any suitable processor, such as amicroprocessor or a computer. Typically, the electronic processor willbe a programmable logic control microprocessor. Also, the electronicprocessor 640 includes, or is connected to, memory includinginstructions for manufacture of particles of the desired composition,which instructions are processable by the electronic processor 640.Furthermore, the memory may include instructions for manufacture ofparticles of a number of different compositions. An operator could theninstruct the electronic processor 640 as to which composition isdesired, and the electronic processor 640 could select and process theappropriate set of instructions for the desired composition. In thisway, the aerosol manufacture facility could be used to manufacturebatches of particles of different compositions, although thoroughcleaning of process equipment would be required between batches ofdifferent compositions.

Also, although FIG. 37 shows automated process control involving all ofthe aerosol heater 602, the precursor liquid supply system 608, thecarrier gas supply system 610, the cooling gas supply system 612 and theaerosol generator 600, it is not necessary, within the scope of thepresent invention, that all of those portions of the aerosol manufacturefacility be automatically controlled, or that any particular operationsbe controlled, but rather only that some operation associated with atleast one of the aerosol heater 602, the precursor liquid supply system608, the carrier gas supply system 610, the cooling gas supply system612 and the aerosol generator 600 be automatically controlled.Preferably, however, at least one operation in each of the aerosolheater 602, the precursor liquid supply system 608, the carrier gassupply system 610, the cooling gas supply system 612 and the aerosolgenerator 600 is automatically controlled at the direction of theelectronic processor 640.

When operation of the aerosol generator 600 is automated, automaticcontrol in the aerosol generator 600 typically includes automaticallyactivating, at the direction of the electronic processor 640, theultrasonic transducers in the aerosol generator 600 during batchinitiation operations and automatically deactivating, at the directionof the electronic processor 640, the ultrasonic transducers during batchtermination operations. The timing for activation and deactivation ofthe ultrasonic transducers in relation to other operations is veryimportant, as discussed more fully below.

As noted previously, control of the concentration of the precursormaterial in the precursor liquid through the addition of additionalliquid vehicle is an important aspect of the present invention. In apreferred embodiment, the concentration control is automated. Thisautomation may be accomplished, for example, through monitoring, by theelectronic processor 640, the concentration of the precursor material inthe precursor liquid supply system 608, or monitoring of one or moreproperties of the precursor liquid which are indicative of concentrationor from which concentration may be calculated.

FIG. 38 shows one embodiment of the precursor liquid supply system 608including automated control of the concentration of the precursormaterial in the precursor liquid, as well as automated control of otherprocess parameters. As shown in FIG. 38, the precursor liquid supplysystem 608 includes two liquid containment vessels, a first vessel 650and a second vessel 652. During the intermediate operations of batchprocessing, both the first vessel 650 and the second vessel 652 containat least some of the precursor liquid. The first vessel 650 acts as aprimary supply source for the precursor liquid and the second vesselacts as a control vessel from which precursor liquid is withdrawn forthe precursor liquid feed 620 supplied to the aerosol generator, and towhich the additional liquid vehicle 636 is added for control ofconcentration of precursor material in the precursor liquid. The secondvessel 652, therefore, typically has a much smaller liquid containmentcapacity than the first vessel 650. Typically, the second vessel 652 hasa capacity of no larger than about 50% of the capacity of the firstvessel. The capacity of the second vessel may, however, be considerablysmaller, such as less than 10% of the capacity of the first vessel. Forexample, the first vessel may have a capacity of about 250 gallons(about 946 liters) and the second vessel a capacity of about 15 gallons(about 57 liters).

During the intermediate operations, with reference to FIGS. 37 and 38,precursor liquid is withdrawn from the first vessel 650 by a pump 654,with a portion of the precursor liquid exiting the pump 654 beingtransferred to the second vessel 652 through a flow control valve 656and a check valve 658. Another portion of the precursor liquid exitingthe pump 654 is recirculated back to the first vessel 650 in arecirculation stream 660. The recirculation stream 660 helps to keep theprecursor liquid in the first vessel 650 thoroughly mixed and to avoidthe development of concentration gradients within the first vessel 650.This is particularly important when the precursor liquid includesprecursor material in the form of suspended particles, as describedpreviously. Mixing in the first vessel may be aided by operation of amixer 662 to drive an impeller 664 located within the first vessel 650.The flow control valve 656 is used to control the transfer of precursorliquid from the first vessel to the second vessel, as discussed below.The check valve 658 prevents inadvertent back flow toward the firstvessel 650, and permits the first vessel 650 to be maintained in asubstantially unpressurized state while the second vessel 652 ispressurized. Maintaining the first vessel 650 in an unpressurized statesignificantly simplifies operations involving the first vessel 650.

Also, during the intermediate operations, precursor liquid is withdrawnfrom the second vessel 652 by a pump 665 for supply to the aerosolgenerator 600 as the precursor liquid feed 620, after passing through aflow control valve 660 and a flow element 668. The precursor liquideffluent 622 from the aerosol generator is returned to the second vessel652. A side stream 670 is withdrawn from the bottom portion of thesecond vessel 652 by a pump 672. The side stream 670 passes through amonitor element 674 and is recirculated to the top portion of the secondvessel 652. The recirculation of the side stream 670 helps to keep theprecursor liquid in the second vessel 652 well mixed and to avoid thedevelopment of concentration gradients within the second vessel 652. Theadditional liquid vehicle 636 passes through a flow control valve 676and a flow element 678 prior to entering the second vessel 652.

The precursor liquid effluent 622 typically involves significant flow.This is because, typically, only a small portion of the precursor liquidfeed 620 is converted to droplets in the aerosol stream during a singlepass through the aerosol generator 600. The recycle ratio for theprecursor liquid fed to the aerosol generator, is typically larger thanabout four to one, more typically larger than about six to one, evenmore typically larger than about eight to one and still more typicallylarger than about ten to one. The recycle ratio is the volumetric ratioof recycled precursor liquid to fresh precursor liquid in the precursorliquid feed 620 (i.e., ratio of rate of flow of precursor liquideffluent 622 to rate of transfer of fresh precursor liquid from thefirst vessel 650 to the second vessel 652). The portion of the precursorliquid feed 620 that exits the aerosol generator 600 in the aerosolstream is typically less than about twenty volume percent of theprecursor liquid feed 620, and more typically less than about fifteenvolume percent, even more typically less than about ten volume percent,and still more typically less than about five volume percent of theprecursor liquid feed 620. The portion of the precursor liquid feed 620exiting the aerosol generator 600 as the precursor liquid effluent 622is typically larger than about eighty volume percent of the precursorliquid feed 620, more typically larger than about eighty-five volumepercent, even more typically larger than about ninety volume percent andstill more typically larger than about ninety-five volume percent of theprecursor liquid feed 620.

FIG. 38 shows major elements for automated process control within theprecursor liquid supply system 608. As will be appreciated, however,additional automated process control features could also be includedwithout departing from the scope of the present invention. Furthermore,the present invention does not require the inclusion of all of theautomated process control features shown in FIG. 38.

As shown in FIG. 38, automated process control involves flow controlvalves 656, 665, 676, and 684, level indicators 680, 682 and 688, themonitor element 674, and the flow elements 668, 678, and 686. Differentcombinations of the process control equipment are used to control thebatch initiation operations, intermediate operations and batchtermination operations, respectively. Communication between the processcontrol equipment and the electronic processor 640 (as shown in FIG.37), which directs the automated control, is via the controller 642. Itwill be appreciated that the controller 642 is shown in several placesin FIG. 38, even though the controller 642 may constitute a single unit.

One of the important control features shown in FIG. 38 is automaticcontrol of addition of the additional liquid vehicle 636 to the secondvessel 652 to control the concentration of precursor material in theprecursor liquid in the second vessel 652, and especially during theintermediate operations.

Automated process control during intermediate operations of batchprocessing will now be described, with reference to FIGS. 37 and 38. Theflow control valve 656 is automatically actuated at the direction of theelectronic processor 640 to control flow of precursor liquid from thefirst vessel 650 to the second vessel 652. The electronic processor 640,via the controller 642, monitors the level of precursor liquid in thesecond vessel 652 based on a signal from the level indicator 680. Theelectronic processor 640 then responsively directs automatic actuationof the flow control valve 656. The flow control valve 656 may beoperated in an open/close mode to either permit or not permit transferof precursor liquid, or may be operated in a proportional mode toincrease or decrease the flow rate of precursor liquid through the flowcontrol valve 656 into second vessel 652. When operated in an open/closemode, the flow control valve 656 is opened when the level in the secondvessel 652 drops below a predetermined level, and the flow control valve656 is closed when the level rises above a predetermined level, so thatthe level in the second vessel is permitted to oscillate between thepredetermined high and low levels. Maintaining the level of theprecursor liquid in the second vessel 652 within a relatively narrowpredetermined range is important to efficient control of theconcentration of precursor material in the precursor liquid, because theconcentration control is easier to accomplish if the level in the secondvessel 652 is relatively constant. For example, the difference betweenthe predetermined high and low levels may be only a few centimeters, orless.

The flow rate of the precursor liquid feed 620 is controlled byautomatic actuation of the flow control valve 666. The electronicprocessor 640 monitors flow rate, via the flow element 668, andresponsively directs control of the flow control valve 666 to maintainthe flow rate to the aerosol generator 600 within a desired range.

In one embodiment, not shown in FIG. 38, the flow rate of the precursorliquid feed 620 may be automatically controlled to maintain a desiredheight of precursor liquid in the reservoir of precursor liquidoverlying ultrasonic transducers in the aerosol generator 600. The flowcontrol valve 620 could be automatically actuated at the direction ofthe electronic processor 640 to increase or decrease the flow to theaerosol generator 600 and, therefore, also increase or decrease theheight of the precursor liquid in the aerosol generator 600. The controlcould include automatic monitoring of the liquid level in the aerosolgenerator 600 by the electronic processor 640, via a level indicator inthe aerosol generator 600.

Referring again to FIGS. 37 and 38, the concentration of precursormaterial in the precursor liquid contained in the second vessel 652 iscontrolled by the addition of the additional liquid vehicle 636 tooffset a tendency of the circulated precursor liquid to otherwiseconcentrate over time. Addition of the additional liquid vehicle 636 iscontrolled by automatic actuation of the flow control valve 676 at thedirection of the electronic processor 640. The electronic processor 640monitors one or more properties of the precursor liquid in the secondvessel 652 via the monitor element 674. The electronic processor 640also monitors the level of the precursor liquid within the second vesselvia the level indicator 682 and the flow of the additional liquidvehicle 636 via the flow element 678. Based on the monitored conditions,the electronic processor 640 directs automatic actuation of the flowcontrol valve 676, as necessary, to add a proper quantity of theadditional liquid vehicle 636 to the second vessel 652. For example, themonitor element 674 may measure the specific gravity, or density, andthe temperature of the precursor liquid contained in the second vessel652. The specific gravity, or density, measurement may be accomplishedwith any suitable density meter, such as a MicroMotion™ coriolis sensor.With the monitored information, in combination with information from thelevel indicator 682, the electronic processor 640 can calculate aconcentration for the precursor material in the precursor liquidcontained within the second vessel 652 and can then calculate a quantityof the additional liquid vehicle 636 to add to maintain theconcentration within a desired range. The flow element 678 then keepsthe electronic processor 640 informed as to the actual quantity of theadditional liquid vehicle 636 that has been added. The flow controlvalve 676 may be operated as an open/close mode to periodically admitthe additional liquid vehicle 636 as required, or may be operated in aproportional mode to continuously vary the flow rate of the additionalliquid vehicle 636. Also, it should be appreciated that the monitorelement 674 could be located at locations other than that shown in FIG.38. For example, the monitor element could be located downstream of thepump 665 to monitor properties of the precursor liquid in the precursorliquid feed 620. Also, the monitor element 774 could be combined withthe flow element 668 into a single element.

Automated process control during batch initiation operations will now bedescribed, with continued reference to FIGS. 37 and 38. Prior tocommencement of batch initiation operations, the first vessel 650 willtypically be substantially empty. Batch initiation operations willtypically commence with an operator inputting instructions to theelectronic processor 640 that a batch is to be prepared of particles ofa selected material. Flow control valve 684 is initially closed and isautomatically actuated to an open position at the direction of theelectronic processor 640 to permit make-up liquid vehicle 690 to enterthe tank. The make-up liquid vehicle is often deionized water. Theelectronic processor 640 monitors the flow of the make-up liquid vehicle690 into the first vessel 650 and directs the flow control valve 684 toa closed position to discontinue flow into the first vessel 650 when apredetermined quantity of the make-up liquid vehicle 690 has been addedto the first vessel 650. The operator adds a predetermined quantity ofprecursor material to the first vessel 650. The precursor material mayinclude only a single material, such as a soluble salt or dispersibleparticles, or may comprise multiple materials, as described previously.The addition of the precursor material may occur after all of themake-up liquid vehicle 690 has been added to the first vessel 650 orbefore all of the make-up liquid vehicle 690 has been added. The mixer662 is activated to turn the impeller 644 to thoroughly mix liquidvehicle and precursor material in the first vessel 650. Also, the pump654 is turned on and flow is established through the recirculationstream 660 to further aid mixing. The flow control valve 656 isinitially in a closed position to prevent flow into the second vessel652. After mixing in the first vessel 650 has proceeded for a timesufficient to adequately mix the liquid vehicle and precursor materialto form the desired precursor liquid, then the flow control valve 656 isautomatically actuated to an open position at the direction of theelectronic processor 640 to permit the flow of precursor liquid into thesecond vessel 652, which is, preferably, initially substantially empty.

After there is an adequate quantity of precursor liquid in the secondvessel 652, circulation of precursor liquid is established through theaerosol generator 600, with the ultrasonic transducers being deactivatedso that no aerosol is being generated in the aerosol generator 600. Toestablish the circulation, the pump 665 is activated to commence theflow of the precursor liquid feed 620 which circulates through theaerosol generator 600 and returns to the second vessel 652 as theprecursor liquid effluent 622. Also, the pump 672 is activated tocommence recirculation of precursor liquid through the recirculationstream 673. In a preferred embodiment, the pump 654, pump 665, pump 672,and mixer 662 are all automatically actuated at the direction of theelectronic processor 640. This embodiment is shown in FIG. 39.

Another embodiment of the precursor liquid supply system 608, includingmajor process components, is shown in FIG. 40. As shown in FIG. 40, aprecursor liquid heater 692 is located between the pump 665 and the flowcontrol valve 666. When the precursor liquid heater 692 is activated,the precursor liquid in the precursor liquid feed 620 is heated prior tointroduction into the aerosol generator 600. Although the precursorliquid heater 692 could be used to heat the precursor liquid at anydesired time, typically the precursor liquid heater is used only duringbatch initiation operations. When circulation of precursor liquid isbeing established through the aerosol generator 600 during batchinitiation operations, as previously described, the precursor liquidheater 692 is automatically turned on at the direction of the electronicprocessor 640. The electronic processor 640 monitors, via a temperatureindicator 694, the temperature of the precursor liquid effluent 622 andthe precursor liquid heater 692 is automatically turned off, at thedirection of the electronic processor 640, when the temperature in theprecursor liquid effluent 622 reaches a predetermined elevatedtemperature. In this manner, the precursor liquid circulating throughthe aerosol generator during the batch initiation operations is at anelevated temperature and, therefore, heats at least a portion of theaerosol generator. This conditions the aerosol generator to simulateoperating conditions during intermediate operations when the ultrasonictransducers are activated and are warming the aerosol generator 600 andthe precursor liquid in the aerosol generator 600. The electronicprocessor 640 also monitors, via a temperature indicator 696, thetemperature of the precursor liquid in the precursor liquid feed 620. Ifthe temperature becomes excessively high, the electronic processor 640can direct that the precursor liquid heater 692 be automatically turnedoff or heat input be reduced.

Referring now to FIG. 41; another embodiment of the precursor liquidsupply system 608, including major process control components, is shown.The embodiment shown in FIG. 41 includes a hopper 698 which containsprecursor material. During the batch initiation operations, the hopperis automatically controlled, at the direction of the electronicprocessor 640, to deliver a specified quantity of the precursor materialto the first vessel 650 during the batch initiation operations. Multiplehoppers could be used for multiple precursor materials, if desired.

Referring once again to FIGS. 37 and 38, automated process control inthe precursor liquid supply system during batch termination operationswill now be described. During the intermediate operations, precursorliquid is transferred from the first vessel 650 to the second vessel 652and, accordingly, the level of the precursor liquid in the first vessel650 drops as the intermediate operations continue. The electroniccontroller 640 monitors, via the level indicator 688, the precursorliquid level within the first vessel 650. When the liquid level in thefirst vessel 650 drops below a predetermined level, the electronicprocessor 640 automatically commences the batch termination operations.

After the batch termination operations are commenced, the pump 654 isautomatically shut off at the direction of the electronic processor toterminate transfer of precursor liquid from the first vessel 650 to thesecond vessel 652. Precursor liquid, however, continues to be withdrawnfrom the second vessel 652 by the pump 665 to supply the precursorliquid feed 620. Because there is no fresh precursor liquid beingintroduced into the second vessel 652, however, the tendency of theprecursor liquid to become more concentrated in the precursor materialover time becomes an even bigger problem. Therefore, during the batchtermination operations, the rate of addition of the additional liquidvehicle 636 will typically be accelerated relative to the rate ofaddition during the intermediate operations. When the level of theprecursor liquid in the second vessel 652 drops below a certain level,as monitored by either level indicator 680 or level indicator 682, theelectronic processor automatically turns off pump 665 and pump 672 andcloses the flow control valve 676, if the flow control valve 676 is notalready closed. Alternatively, the pump 665 could be automaticallyturned off, at the direction of the electronic processor 640 when theelectronic processor 640 determines that the concentration of precursormaterial in the liquid vehicle has reached an undesirably high level.

Although the precursor liquid supply system 608 has been described inFIGS. 38-41 with reference to the use of two vessels, the liquid supplysystem could be operated with only a single vessel, if desired. If onlya single vessel is used, then that vessel would act as primary supplyvessel and a control vessel, applying the principles as discussed withrespect to FIGS. 38-41. With the present invention, however, it ispreferred that the precursor liquid supply system 608 include twovessels, as described with reference to FIGS. 38-41.

FIG. 42 shows a schematic of one embodiment of the carrier gas supplysystem 610, including major process control components. Referring now toFIGS. 37 and 42, automated control of the carrier gas supply system 610will be described. With reference to FIGS. 37 and 42, duringintermediate operations of batch processing, a main carrier gas feed 700is divided into a plurality of carrier gas feed streams 702, with eachcarrier gas feed stream 702 providing a portion of the carrier gas 624to the aerosol generator 600. For example, each of the carrier gas feedstreams 702 could provide a different portion of the carrier gas 624 toa different location within the aerosol generator 600, to ensure gooddistribution of the carrier gas 624 in the aerosol generator 600. Theflow of carrier gas in each of the carrier gas feed streams 702 isindependently automatically controlled at the direction of theelectronic processor 640 through automatic actuation of the appropriateflow control valve 704. The electronic processor 640 monitors flowthrough each of the carrier gas feed streams 702 via the flow element706. Based on flow information from the flow element 702, the electronicprocessor directs control of the corresponding flow control valve 704accordingly. Independent control of the carrier gas feed streams 702permits more precise control of carrier gas delivery to the aerosolgenerator 600. Also, the independent control of each of the carrier gasfeed streams 702 allows flexibility to deliver carrier gas to someportions of the aerosol generator 600 and not to other portions of theaerosol generator 600. Therefore, if part of the aerosol generator mustbe shut down because of an operating problem, other portions of theaerosol generator can continue to operate to generate the aerosolstream. For example, the aerosol generator could include the ultrasonictransducers subdivided into independently activatable groups, with atleast one group corresponding with each of the carrier gas feed streams702.

With continued reference to FIGS. 37 and 42, automated control of thecarrier gas supply system 610 during the batch initiation operationswill be described. Initially all of the flow control valves 704 areclosed. At the direction of the electronic processor 640, each of theflow control valves 704 is automatically opened to initiate the flow ofcarrier gas through the carrier gas feed streams 702. During batchtermination operations, the electronic processor automatically directsclosure of each of the flow control valves 704 to discontinue the supplyof carrier gas through the carrier gas feed streams 702.

FIG. 51 shows a schematic of another embodiment of the carrier gassupply system 610 in which the additional liquid vehicle 636 is added tothe carrier gas. FIG. 51 is the same as FIG. 42, except that the maincarrier gas feed 700 is heated in a heater 708 and the additional liquidvehicle 636 is then added to the main carrier gas feed 700. Theadditional liquid vehicle 636 is preferably added in an amount that willsubstantially saturate the main carrier gas feed 700 with vapor of theliquid vehicle. Heating of the main carrier gas feed 700 is done toincrease the quantity of vapor of the liquid vehicle that may beaccommodated by the main carrier gas feed 700 when saturated. Withreference to FIGS. 37 and 51, the temperature of the main carrier gasfeed 700 after the heater 708 is preferably approximately equal to, orslightly higher than, the temperature of the aerosol stream beinggenerated in the aerosol generator 600, so that the carrier gas 624 willbe substantially saturated in the liquid vehicle at the conditions ofaerosol generation, to reduce or substantially prevent vaporization inthe aerosol generator 600 of liquid vehicle from the precursor liquidfeed 620 fed to the aerosol generator 600.

Also, although a preferred embodiment of the method of the presentinvention includes a circulating precursor liquid, it is possible tooperate without precursor liquid circulation. For example, when thecarrier gas 624 is saturated with vapor of the liquid vehicle, as justdescribed, then the loss of liquid vehicle from precursor liquid in theaerosol generator 600 may be small enough to avoid circulationaltogether. In one embodiment, the precursor liquid could be fed to theaerosol generator 600 at a rate substantially equal to the rate ofdroplet generation to form the aerosol stream, with no precursor liquideffluent stream 622 exiting the aerosol generator. As another example,circulation could also be avoided by processing a more dilute precursorliquid, that then concentrates, in a steady state fashion in the aerosolgenerator 600 to a desired concentration. The precursor liquid would befed to the aerosol generator 600 at a rate substantially equal to therate consumption in the aerosol generator 600, including consumption toproduce droplets for the aerosol stream and to saturate the carrier gasin the aerosol generator 600 with vapor of the liquid vehicle.

FIG. 43 shows a schematic of one embodiment of the cooling gas supplysystem 612, including some major process control features. Referring toFIGS. 37 and 43, automated control of the cooling gas supply system willbe described. During intermediate operations, a blower 710 suppliescooling gas, typically air, through a flow control valve 712 to providethe cooling gas feed 626 to the aerosol cooler 604. The flow controlvalve 712 is a three-way valve and excess cooling gas is vented via avent stream 714. The electronic processor 640 monitors, via a flowelement 716, the flow of the cooling gas feed 626. The flow controlvalve 712 is automatically actuated, based on directions from theelectronic processor 640, to vary the relative quantities of the coolinggas in the cooling gas feed 626 and the vent stream 714, to maintain theflow rate of the cooling gas feed 626 within a desired range. During thebatch initiation operations, the blower 710 is initially idle and isautomatically turned on at the direction of the electronic processor640. During batch termination operations, the blower 710 isautomatically turned off at the direction of the electronic processor640, to discontinue flow of the cooling gas feed 626.

As one alternative to the embodiment described with reference to FIGS.37 and 43, the cooling gas feed 626 could be supplied to aerosol cooler604 by pulling a vacuum on the aerosol manufacture facility, rather thansupplying the cooling gas feed 626 under a positive pressure as shown inFIG. 43. Likewise, the supply of the carrier gas 624 could also besupplied by pulling a vacuum on the system. For example, a blower couldbe located downstream of the particle collector 606 to pull a vacuumthrough the aerosol generator 600, the aerosol heater 602, the aerosolcooler 604 and the particle collector 606. The carrier gas supply system610 could include a vacuum valve that permits flow of the carrier gas624 when the pressure across the vacuum valve reaches a predeterminedlevel as the vacuum develops in the system. The flow rate of the carriergas 624 to the aerosol generator 600 could then be automaticallycontrolled using a control system similar to that shown in FIGS. 42 or51, but with operation at a vacuum. Likewise, the cooling gas supplysystem 612 could include a vacuum valve and automated flow controldownstream of the vacuum valve.

FIG. 44 shows one embodiment of the aerosol heater 602 comprising a tubefurnace 720, including eight separate heating zones, numbered 1 through8. Heating zones 1 and 2 are adjacent the inlet to the tube furnace 726and heating zones 7 and 8 are adjacent the outlet from the tube furnace720. Each of the heating zones is associated with one or more heatingelements that is independently controllable to independently controlheat input into each of the heating zones. Each of heating zones 3,4,5and 6 cover a full circumferential area of the tube 722 over someportion of the longitudinal dimension of the tube 722. Heating zones 1and 2 are directly opposing and each cover a portion extending around acircumferential half of the tube 722, with heating zone 1 covering acircumferential top half and heating zone 2 covering a circumferentialbottom half of the tube 722. Likewise, heating zones 7 and 8 each covera portion extending around only a circumferential half of the tube 722,similar to the arrangement of heating zones 1 and 2. Heating zones 1 and2, are, therefore, directly opposing each other in a directionsubstantially perpendicular to the direction of flow through the tubefurnace 720. A similar relationship exists between heating zones 7 and8. As noted, each of the heating zones is independently controllable.FIG. 45 shows a simplified cross-section through heating zones 1 and 2of the tube furnace 720, showing the location of heating zones 1 and 2in the interior of the tube 722. Heating zone 1 is heated by a heatingelement 724 while heating zone 2 is independently heated by an opposingheating element 726.

With reference to FIGS. 37, 44 and 45, automated control of heat inputinto the aerosol heater 602 will be described. During intermediateoperations of batch processing, the aerosol stream flows through theinterior of tube 722 of the tube furnace 720. One or more of the heatingzones are individually heated by heating elements corresponding withthose heating zones. The electronic processor 640 automaticallymonitors, via the temperature indicator 724, the temperature at somelocation within the tube furnace 720. Typically, the temperature ismonitored at the outer surface of the tube 720 by a thermocouple locatedat the outer surface. Based on the monitored temperature information,the electronic processor 640 automatically directs the tube furnace 720to control the heat input of the heating zones. Although only a singletemperature indicator 724 is shown in FIG. 44, typically a number oftemperature indicators would be used, with at least one for each heatingzone, and the electronic processor would automatically direct control ofheat input into each of the heating zones accordingly. Furthermore, thetube furnace 720 is typically oriented so that the flow of the aerosolstream through the tube 722 is in a substantially horizontal direction.With such a configuration, there is a tendency of droplets or particles,as the case may be, in the aerosol stream to vertically rise due tobuoyancy forces caused by heating of the aerosol stream. To at leastpartially accommodate this effect, it is typically desired to have ahigher heat input into heating zone number 2 than into heating zonenumber 1. For example, heat input into heating zone 2 could be threetimes the heat input in zone 1. In an extreme situation, heat inputcould be only into zone 2 with no heat input into zone 1, with zone 1then being heated through convective heating from zone 2. During batchinitiation operations, heat input into the heating zones is either zeroor at a reduced level. Heat input is automatically increased, however,at the direction of the electronic processor 640 to cause thetemperature within the tube 722 to increase, prior to flowing theaerosol stream through the tube 722. During the batch terminationoperations, heat input into the tube furnace 720 is automaticallyreduced or terminated, to automatically decrease the temperature withinthe tube 722. This is typically done after the flow of the aerosolstream through the tube 722 has been discontinued.

FIG. 46 shows another embodiment of the aerosol heater 602 including thetube furnace 720. Temperature control is as described previously withrespect to FIGS. 44 and 45. With reference to FIGS. 37 and 46, the endsof the tube furnace are attached to end caps 728, which provide for aflange connection to conduits connecting with the aerosol generator andthe aerosol cooler. During batch processing, the end caps 728 may becooled with a cooling liquid 730, such as water, circulated through atleast a portion of each end cap 728. During normal manufactureconditions present during the intermediate operations, the electronicprocessor typically maintains the flow control valves 732 in a closedposition so the cooling fluid 730 is not flowing to the end cap 728.During the intermediate operations when the aerosol stream is flowingthrough the tube 722, there is typically no need to cool the end cap728. During batch initiation operations, however, when the temperaturein the furnace is being increased, and before the flow of carrier gashas been initiated, the electronic processor 640 directs automaticactuation of the flow control valves 732 to an open position to permitthe cooling liquid 730 to cool the end caps 728. During batchtermination operations, the electronic processor 640 may direct that theflow control valves 732 once more be automatically actuated into an openposition to commence cooling of the end caps 728, while the temperaturein the furnace is reduced to a desired level after flow of the carriergas is discontinued through the tube furnace 720. Opening and closing ofthe flow control valves 732 could be directed by the electronicprocessor 640 based on any suitable input. For example, the flow controlvalves 732 could be opened and closed at specific times during batchinitiation operations and batch termination operations, or could beopened and closed based on a monitored condition, such as a monitoredtemperature in the vicinity of one or both of the end caps 728.

Referring now to FIGS. 46 and 47, one design for the end caps 728 isshown. As shown at FIGS. 46 and 47, the end caps 728 include a flangebody portion 736 with a recess 738 about the edge in which a small tube740 is disposed. The tube 740 provides a flow path for the coolingliquid 730 to circulate through the end caps 728 when being cooled. Thetubes 740 are typically copper tubes for efficient heat transfer.

Referring now to FIG. 49, another embodiment of the aerosol manufacturefacility is shown in which an electronic processor 640 is used to directcontrol of at least portions of batch processing in the aerosolmanufacture facility. As shown in FIG. 49, the electronic processor 640communicates, via the controller 642, with the cooling fluid supplysystem 630, in addition to communication with the carrier gas supplysystem 610, the precursor liquid supply system 608, the cooling gassupply system 612, the aerosol heater 602 and the aerosol generator 600.

FIG. 50 show one embodiment of the cooling liquid supply system 630,including some major automated process control features. Referring nowto FIGS. 49 and 50, automated control of the cooling liquid supplysystem 630 will be described. During intermediate operations of batchprocessing, the cooling liquid feed 632 is withdrawn from a coolingliquid tank 744 by a pump 746 and passes through a flow control valve748. The cooling liquid effluent 634 is returned to the cooling liquidtank 744 for recirculation. Cooling liquid in the cooling liquid tank744 is cooled via cooling coils 750. Make-up cooling liquid 752 is addedas required. The cooling liquid is typically deionized water. During theintermediate operations, the electronic processor 640 monitors, via atemperature indicator 754, the temperature of cooling liquid in thecooling liquid effluent 634 and the electronic processor 640, based onthe monitored temperature information, automatically actuates the flowcontrol valve 748, as necessary, to increase or decrease the flow rateof the cooling liquid feed 632. During batch initiation operations, thepump 746 is initially in the off position. The pump 646 is automaticallystarted at the direction of the electronic processor 640 to commence theflow of the cooling liquid feed 632. During the batch terminationoperations, the pump 746 is automatically shut off at the direction ofthe electronic processor 640, to terminate the flow of the coolingliquid feed 632.

In one embodiment for the cooling liquid supply system 630, coolingliquid could be supplied, during the intermediate operations, toelectronic driver circuits driving the ultrasonic transducers of theaerosol generator 600, to cool the driver circuits to preventoverheating. Cooling liquid to the driver circuitry may be automaticallycontrolled at the direction of the electronic processor 640, in a mannersimilar to control of the cooling liquid feed 632 to cool the ultrasonictransducers.

Referring now to FIG. 52, another embodiment is shown of the aerosolmanufacture facility. This embodiment is the same as that shown in FIG.37, except that the electronic processor 640 communicates, via thecontroller 642, with a cooling unit 756. Operation of the cooling unit756 is automatically controlled at the direction of the electronicprocessor 640. The cooling unit 756 will typically be automaticallyactivated during the batch initiation operations and will beautomatically deactivated during the batch termination operations.During intermediate operations, the cooling unit 756 will typically beoperated when the aerosol generator 600 is generating the aerosolstream. The purpose of the cooling unit 756 is to cool at least aportion of the conduit 614, to prevent overheating of the aerosol streamflowing in the conduit 614 between the aerosol generator and the aerosolheater 602. The cooling unit 756 is typically a fan or blower blowingair on the conduit 614 to effect the desired cooling.

With continued reference to FIG. 52, in a preferred embodiment, thecooling unit 756 cools the first conduit portion 760 and substantiallydoes not cool the second conduit portion 762. The first conduit portion760 directs flow in a substantially vertical direction and the secondportion, which is on the other side of the bend in the conduit 614,directs the flow of the aerosol stream in a substantially horizontaldirection. By cooling the first conduit portion 760, excessivevaporization of liquid vehicle from droplets in the aerosol stream isprevented, allowing oversize droplets and liquid collecting on the wallsof the first conduit portion 760 to drain back into the aerosolgenerator 600. However, because the second conduit portion 762 issubstantially not cooled, heat from the aerosol heater 602 will tend tovaporize liquid vehicle from the droplets in the aerosol stream. Underthese conditions, a situation is prevented where, otherwise, liquid maybuild up on the walls at the entrance of the aerosol heater 602, whichmay cause significant problems. In some instances, it may be desirableto insulate the second conduit portion 762 to prevent heat loss and topromote the desired vaporization of liquid vehicle from the droplets inthe aerosol stream. Furthermore, in a preferred embodiment, thetemperature of the wall of the first conduit portion 760 is monitored,with a temperature sensor, by the electronic processor 640, and thecooling unit 756 is turned on or off as necessary. Normally, the coolingunit is turned off and is turned on only if the wall temperature exceedsa predetermined value. The cooling unit 656 may also provide benefitsduring batch initiation and/or batch termination operations. Forexample, when the temperature in the aerosol heater 602 is beingincreased during batch initiation operations, without the flow ofcarrier gas, the cooling unit 756 may be turned on to preventoverheating of the conduit 614. Likewise, the cooling unit 756 may beturned on to cool the conduit 614 during batch termination operationsafter the flow of carrier gas is discontinued.

FIG. 61 shown another embodiment of the aerosol manufacture facility.FIG. 61 is the same as FIG. 37, except that the electronic processor 640is also communicating, via the controller 642, with an aerosol monitor648 located at the exit from the aerosol generator 600. Duringintermediate operations, the aerosol stream passes through the aerosolmonitor 648. In the aerosol monitor 648, a light source, such as a neonor other source, directs a light beam across at least a portion of theflowing aerosol stream toward a light detector. The amount of lightdetected by the light detector provides information concerning thedensity of the liquid droplets in the aerosol stream. In the embodimentshown in FIG. 61, the electronic processor 640, during the intermediateoperations, monitors, via the aerosol monitor 648, the density of theaerosol stream exiting the aerosol generator 600. The electronicprocessor 640 may then process the monitored aerosol density informationand provide useful feedback and/or control. For example, when theelectronic processor 640 identifies an anomaly in the density of theaerosol stream, an alarm could be activated to alert an operator, sothat the operator could investigate the cause of the anomaly and makeadjustments or repairs as necessary. Also, the electronic processor 640could use the monitored aerosol density information to effect processcontrol. For example, based on the density information, the electronicprocessor 640 could, during the intermediate operations, automaticallydirect an increase or decrease of flow in the precursor liquid stream620, and/or the flow rate of the carrier gas 624 to optimize the densityof the aerosol stream. During batch termination operations, theelectronic processor 640 could direct automatic discontinuance of purgeoperations after the aerosol monitor 648 indicates that there is no moreaerosol flowing from the aerosol generator 600, indicating that thesystem has been adequately purged of remaining aerosol.

Although the aerosol manufacture method has been described as generallyending with collection of the particles in the particle collector, insome embodiments additional processing may be performed after particlecollection. For example, if it is desired to further modify thecomposition or the morphology of the particles, the particles may besubjected to a post-collection anneal, or other operation at elevatedtemperature. During the post-collection anneal, components in theparticles may react to alter the chemical composition of the particle,or one or more phases within the particles may be recrystallized orreconfigured. The anneal may be performed, for example in a rotary kiln.

Referring again to FIG. 33, the sequence for processing of a batchbegins with batch initiation operations as a first stage, passes throughintermediate operations as a second stage, and ends with batchtermination operations as a third stage. The particular sequences ofspecific operations, or steps, within each of these stages may be variedconsiderably and still be within the scope of the present invention. Inthat regard, however, the activation of the ultrasonic transducersduring the batch initiation operations and the deactivation of theultrasonic transducers during the batch termination operations arecritical steps, and it is necessary that certain steps be performedduring the batch initiation operations prior to activation of theultrasonic transducers and the certain steps during the batchtermination operations occur after deactivation of the ultrasonictransducers, as described in more detail below.

FIG. 53 is a flow diagram for one embodiment for a sequence of stepsduring the batch initiation operations. Referring to FIGS. 37 and 53,the first step is to prepare the precursor liquid batch. This typicallycomprises adding the liquid vehicle and the precursor material together,with appropriate mixing, to prepare the desired precursor liquid in abatch size desired for processing. It will be appreciated, however, thatbatches of the precursor liquid could be acquired in a pre-preparedstate, in which case the batch initiation operations would not includepreparation of the precursor liquid batch.

The next step shown in FIG. 53 is to establish precursor liquidcirculation. This typically involves commencing to supply the precursorliquid feed 620 to the aerosol generator 600 from the precursor liquidsupply system 608 and receiving back to the precursor liquid supplysystem 608 the precursor liquid effluent 622 from the aerosol generator600. After circulation of the precursor liquid to the aerosol generator600 has been established, the next step is to increase the temperaturewithin the aerosol heater 602 to some elevated temperature. This istypically accomplished by increasing heat input into the aerosol heater602. For example, when using a furnace as the aerosol heater 602, heatinput is increased into one or more of a plurality of heating zones inthe furnace, as previously described.

The next steps, as shown in FIG. 53, are to commence the carrier gassupply and to commence the cooling gas supply. These steps are shown asoccurring substantially simultaneously. Commencing the carrier gassupply typically involves establishing flow of the carrier gas 624 tothe aerosol generator 600 from the carrier gas supply system 610.Commencing the cooling gas supply typically involves beginning the flowof the cooling gas feed 626 to the aerosol cooler 604 from the coolinggas supply system 612.

The next step shown in FIG. 53 is to condition the equipment. Thisinvolves flowing the carrier gas, without generation of the aerosolstream, through the flow path comprising the aerosol generator 600, theaerosol heater 602, the aerosol cooler 604 and the particle collector606. The aerosol heater 602 is at an elevated temperature and heats theflowing carrier gas. In the aerosol cooler 604, the hot carrier gas ismixed with the cooling gas feed 626 and then passes to the particlecollector 606. Because the gas flowing through the particle collector606 is at an elevated temperature, the flowing gas will heat at leastportions of the particle collector 606. The effect of this conditioningstep is to simulate conditions that will exist later, during theintermediate operations, after aerosol generation has commenced. Forexample, the aerosol cooler 604 and the particle collector 606 arewarmed, under dynamic conditions, to a temperature simulating operatingtemperatures during the subsequent intermediate operations. Also, thefurnace is conditioned in a dynamic state with flowing gas to simulateconditions that will exist during the intermediate operations.

The next step, as shown in FIG. 53, is to activate the ultrasonictransducers. This is accomplished by supplying electrical power to theultrasonic transducer driver circuits to drive the ultrasonictransducers. Once the ultrasonic transducers have been activated,generation of the aerosol stream in the aerosol generator 600 commences.Because the generation of the aerosol stream does not commence untilafter the equipment has been conditioned, as previously discussed, thesystem is initially ready to produce particles under a steady state orquasi-steady state situation. This has the effect of reducing transitoryeffects in the system in the early stages of particle manufacture andreduces the possibility that substandard particles will be produced inthe early stages. This is important because such substandard particlescan contaminate an otherwise high quality batch, or could require thatinitial particles that are produced be discarded or subjected tocumbersome recycling operations. After activation of the ultrasonictransducers, the batch processing will proceed through the intermediateoperations.

FIG. 54 shows a flow diagram for another embodiment for a sequence ofsteps during batch initiation operations. The sequence is the same asthat shown in FIG. 53, except that two pressure test steps have beenadded. The first pressure test is conducted after preparation of theprecursor liquid batch and before establishing the precursor liquidcirculation. The first pressure test involves pressuring the flow pathfor the aerosol stream with the carrier gas and monitoring thepressurized flow path to identify leaks. The pressure test is primarilyfor safety, to ensure consistent flows throughout the system and toprevent losses. If the system fails the pressure test, then the batchinitiation operations may be terminated and the source of the leakidentified and fixed.

The second pressure test step shown in FIG. 54 follows the step ofconditioning the equipment. For the second pressure test, the coolinggas supply and the carrier gas supply are temporarily interrupted andthe flow path is again pressurized with carrier gas and the pressuremonitored to identify leaks. The second pressure test is important toidentify leaks that may develop after the equipment has reached anelevated temperature, that were not identified during the first pressuretest. If the second pressure test fails, then the batch initiationoperations will be terminated so that the source of the leak can beidentified and fixed.

Referring now to FIG. 55, a flow diagram is shown of another embodimentof a sequence of steps for batch initiation operations. FIG. 55 is thesame as FIG. 53, except that a step has been included to commencecooling liquid supply. This step is shown as being substantiallysimultaneous with establishing precursor liquid circulation. Referringnow to FIGS. 49 and 55, commencing cooling liquid supply involvesestablishing the flow of the cooling liquid feed 632 from the coolingliquid supply system 630 and the return of the cooling fluid effluent634 back to the cooling liquid supply system 630.

Referring now to FIG. 56, a flow diagram is shown of another embodimentfor a sequence of steps during batch initiation operations. FIG. 56 isthe same as FIG. 53, except that steps have been included relating toheating of the precursor liquid. Referring to FIGS. 37 and 56, after thestep of establishing precursor liquid circulation, the next step is tocommence heating precursor liquid. This is typically done by heating ofprecursor liquid in the precursor liquid supply system 608 so that theprecursor liquid feed 620 supplied to the aerosol generator 600 is at anelevated temperature. By heating the precursor liquid, circulatingprecursor liquid in the aerosol generator 600 simulates an elevatedtemperature that will exist later during intermediate operations whenthe aerosol stream is being generated in the aerosol generator 600.Also, the heated precursor liquid will warm at least portions of theaerosol generator 600, again, simulating operation during intermediateoperations. As shown in FIG. 56, after the step of conditioning theequipment, the next step is to terminate heating of the precursorliquid. During the step of conditioning the equipment, as noted, theheated precursor liquid warms at least a portion of the aerosolgenerator 600. After the equipment has been sufficiently conditioned,the heating of the precursor liquid is terminated and the ultrasonictransducers are then activated to commence generation of the aerosolstream in the aerosol generator 600. At least some of the energy fromthe ultrasonic transducers results in heating of the circulatingprecursor liquid, so that the heating of the precursor liquid istypically no longer required.

With reference to FIGS. 37,38 and 56, it should be noted thatdiscontinuance of heating the precursor liquid might not always berequired or desirable. For some precursor liquid compositions, it may bedesirable to maintain the precursor liquid at a temperature that ishigher than that which would otherwise exist during the intermediateoperations. Also, the electronic processor 640 could continuouslymonitor the temperature of the precursor liquid effluent 622 and couldautomatically commence heating of the precursor liquid feed 620 wheneverthe monitored temperature drops below a predetermined level and couldautomatically discontinue the heating whenever the monitored temperaturedrops below a predetermined level.

Referring to FIG. 57, a flow diagram is shown of yet another embodimentfor a sequence of steps during batch initiation operations. FIG. 57 isthe same as FIG. 53, except that steps have been included concerningcooling of end caps on the aerosol heater. Referring to FIGS. 37, 46 and57, after the precursor liquid circulation has been established, thenext steps, shown as being performed substantially simultaneously, areto increase the heater temperature and to commence cooling the end caps.Commencement of cooling the end caps comprises establishing flow of acooling fluid through at least a portion of the end caps to cool the endcaps and the terminal portions of the aerosol heater 602. The purpose ofcooling the end caps is that without the cooling, the temperature at theterminal ends of the aerosol heater 602 could become excessively high,and could damage gaskets in connections between the aerosol heater andadjacent flow equipment. As seen in FIG. 57, the step precedingconditioning of the equipment is to terminate cooling the end caps. Thisis because after the carrier gas supply has commenced, the carrier gasflowing through the aerosol heater 602 will typically cool the terminalportions of the aerosol heater 602 by a sufficient amount so thatcooling of the end caps is no longer required. Typically, it is notnecessary to cool the end caps when particles are being produced,although the end caps may be cooled, if desired. For example, theelectronic processor 640 could monitor the temperature in the vicinityof the end caps via a temperature probe, and cooling of the end capscould be automatically commenced whenever the monitored temperatureexceeds a predetermined value and automatically terminated whenever themonitored temperature falls below a predetermined value.

Referring now to FIG. 58, a flow diagram shows one embodiment of asequence of steps for batch termination operations. Referring to FIGS.37 and 58, the first step in the batch termination operations is toexhaust the precursor liquid supply. This involves emptying, to theextent practical, the precursor liquid supply system 608 of as much ofthe precursor liquid as possible while continuing to generate theaerosol stream in the aerosol generator 600. Typically, the initiationof the batch termination operations will be triggered by some monitoredcondition within the precursor liquid supply system 608, such as thelevel of precursor liquid remaining in a vessel within the precursorliquid supply system 608.

The next step, as shown in FIG. 58, is to deactivate the ultrasonictransducers. This step involves terminating the supply of electricalpower to the ultrasonic transducer driving circuits. Deactivation of theultrasonic transducers terminates the generation of the aerosol streamin the aerosol generator 600.

The next step, as shown in FIG. 58, is to purge the flow path of theaerosol stream. As noted previously, this flow path includes the aerosolgenerator 600, the aerosol heater 602, the aerosol cooler 604 and theparticle collector 606. The purge is typically accomplished with thecarrier gas, but a purge gas of a different composition could be used,if desired. The purpose of the purge is to remove any remaining aerosolfrom the aerosol generator 600 and downstream equipment. The purge maybe conducted for a predetermined time, or for passage of a predeterminedvolume of purge gas, sufficient to remove any remaining aerosol, or maybe terminated based on monitored conditions within the stream flowingthrough the flow path. For example, the concentration of nitrogen oxidesdownstream of the aerosol heater 602 could be monitored when theprecursor liquid had included a precursor material of nitrate salts.

The next steps, as shown occurring substantially simultaneously in FIG.58, are to terminate the carrier gas supply and to terminate the coolinggas supply. Terminating the carrier gas supply involves terminating theflow of the carrier gas 624 from the carrier gas supply system 610 tothe aerosol generator 600. Terminating the cooling gas supply involvesterminating the cooling gas feed 626 from the cooling gas supply system612 to the aerosol cooler 604.

Referring now to FIG. 59, a flow diagram is shown including anotherembodiment of a sequence of steps for batch termination operations. FIG.59 is the same as FIG. 58, except that a step of terminating coolingliquid flow has been added after the step of deactivating the ultrasonictransducers. With reference to FIGS. 49 and 59, the sequence of steps asshown in FIG. 59 would be appropriate, for example, when the ultrasonictransducers in the aerosol generator 600 are being cooled by the supplyof the cooling liquid feed 632 from the cooling liquid supply system630. Terminating the cooling liquid flow involves terminating the supplyof the cooling liquid feed 632 from the cooling liquid supply system630.

Referring now to FIG. 60, a flow diagram is shown of another embodimentof a sequence of steps for batch termination operations. FIG. 60 is thesame as FIG. 58, except that steps are included concerning the coolingof end caps on the aerosol heater. FIG. 60 shows a step of commencingcooling of end caps occurring substantially simultaneously with reducingthe temperature in the aerosol heater. The commencement of cooling endcaps is similar to that discussed previously with respect to batchinitiation operations. The circulation of a cooling liquid through theend caps is established to prevent terminal portions of the aerosolheater from becoming too hot, which could otherwise occur since carriergas is no longer flowing through the aerosol heater. The next step, asshown in FIG. 60, is to terminate cooling of the end caps. This involvesterminating the circulation of the cooling liquid in the end caps at atime when there is no longer a danger of excessive heat build-up in theterminal portions of the aerosol heater.

The sequences of steps for batch initiation operations and batchtermination operations as shown in FIGS. 53-60 are only preferredprocessing sequences for various embodiments. The present invention,however, is not-limited to the specific embodiments shown in FIGS. 53-60or to the specific order of the sequence of steps as shown in FIGS.53-60, except that during batch initiation operations, certain stepsmust occur prior to activation of the ultrasonic transducers and duringbatch termination operations, certain steps must occur afterdeactivation of the ultrasonic transducers. For example, with referenceto FIG. 53, activation of the ultrasonic transducers must ordinarily bethe last step of those shown, but the preceding steps may be reorderedin any convenient manner. For example, the temperature of the aerosolheater could be increased prior to establishing circulation of theprecursor liquid. With reference to FIG. 54, again the step ofactivating the ultrasonic transducers must ordinarily be the last stepof those shown, but the preceding steps may be reordered in anyconvenient manner. For example, the first pressure test could follow thestep of establishing precursor liquid circulation. Also, the steps ofcommencing the carrier gas supply and the cooling gas supply need notoccur substantially simultaneously. Referring now to FIG. 55, the stepof activating the ultrasonic transducers must ordinarily be the laststep, except that the step of commencing supply of the cooling liquidcould occur after activation of the ultrasonic transducers. Also, othersteps could be reordered in any convenient manner. For example,commencing the cooling liquid supply could occur at a later point in thesequence. Referring now to FIG. 56, the step of activating theultrasonic transducers must ordinarily be the last step, except that thestep of terminating the heating of the precursor liquid could followactivation of the ultrasonic transducers. Also, other steps could bereordered in any convenient manner. Referring now to FIG. 57, the stepof activating the ultrasonic transducers must ordinarily be the laststep, except that the step of terminating the cooling of the end capscould occur after the step of activating the ultrasonic transducers. Theother steps could be reordered in any convenient manner. Referring nowto FIG. 58, the step of deactivating the ultrasonic transducers mustordinarily occur prior to the subsequent listed steps. The subsequentsteps could, however, be reordered as convenient. For example, the stepof reducing the heater temperature could follow the step of terminatingthe precursor liquid supply. Referring now to FIG. 59, those steps shownas following deactivation of the ultrasonic transducers must ordinarilyfollow that step, except that the step of terminating the cooling liquidflow could occur prior to deactivation of the ultrasonic transducers.Other steps could be reordered as convenient. For example, the precursorliquid supply could be terminated prior to reducing the heatertemperature. Referring now to FIG. 60, deactivation of the ultrasonictransducers must ordinarily occur prior to the other listed steps. Theother steps may, however, be reordered as convenient. For example, thestep of commencing to cool the end caps could occur prior to reducingthe temperature in the aerosol heater, and the step of terminating theprecursor liquid could occur prior to any of the steps of terminatingthe cooling of the end caps, commencing the cooling of the end caps, orreducing the heater temperature. Also, other reordering of the steps isalso possible besides those specifically noted above.

As described previously, the intermediate operations typically includesteady state or quasi-steady state manufacture of particles. As noted,however, it may be desirable to have periodic planned, or unplanned,interruptions of the steady state or quasi-steady state conditions tocorrect a problem identified with particle manufacture or for periodicmaintenance or removal of accumulated particulate product. When themanufacture is interrupted during the intermediate operations,initiating the interruption is somewhat analogous to batch terminationoperations and resuming production following the interruption issomewhat analogous to batch initiation operations. Therefore, the priordiscussions concerning batch termination operations and batch initiationoperations are relevant to temporary interruptions occurring duringintermediate operations, suitably modified to fit the particularsituation. For example, when interrupting production during intermediateoperations, it will be necessary to deactivate the ultrasonictransducers, and typically also to temporarily terminate the supply ofcarrier gas to the aerosol generator and of cooling gas to the aerosolcooler. Circulation of precursor liquid and of cooling liquid to thegenerator, if used, could also be temporarily terminated. Furthermore,it may be desirable to lower the temperature in the furnace below theoperating temperature present during particle manufacture. Whencommencing production at the end of an interruption, the system would beconditioned to bring it up to temperature, if necessary, and the flowsof all the fluid streams would be reinitiated and the ultrasonictransducers again activated.

As noted previously, a significant aspect of the present invention isthe automation of one or more operations during the batch processing. Inthat regard, any of the steps occurring during the batch initiationoperations, intermediate operations or batch termination operations canbe automatically controlled at the direction of the electronicprocessor. Although it is only necessary, within the scope of thepresent invention, that at least one operation be automated, it ispreferred that substantially all of the operations be automated. In thatregard, any or all of the steps shown in any of FIGS. 53-60 may beautomatically controlled at the direction of the electronic processor,including transitions between steps. Furthermore, preferably,transitions between the batch initiation operations, the intermediateoperations and the batch termination operations are automaticallycontrolled at the direction of the electronic processor.

It should be recognized that FIGS. 53-60 show various embodiments forthe sequence of steps occurring during the batch processing of thepresent invention. The present invention, however, is not limited to thespecific embodiments exemplified. For example, any of the steps shown inany one of FIGS. 53-60 may be combined, in any combination, with anyother step or sequence of steps of any other embodiments of FIGS. 53-60,so long as the combination is not inconsistent with the description ofthe invention provided herein. Furthermore, any of the features in anyone of FIGS. 31, 32, 34, 35, 36, 37, 49, 51, and 52 may be combined, inany combination, with any of the other features shown in those figures,so long as the combination is not inconsistent with the description ofthe invention provided herein. Also, various embodiments for theprecursor liquid supply system are shown in FIGS. 38-41. The inventionis not limited to these specific embodiments. Furthermore, any featureshown in any one of FIGS. 38-41 may be combined, in any combination,with other features shown in any of those Figures in the precursorliquid supply system, so long as the combination is not inconsistentwith the description of the invention provided herein. Moreover, FIGS.42, 43, 44, 45, 46, 47, 48, 50 and 51 show specific embodiments for thecarrier gas supply system, the cooling gas supply system, the aerosolheater, the end caps, and the cooling liquid supply system. Theinvention is not, however, limited to these specific embodiments.Furthermore, any of the disclosed embodiments of the liquid supplysystem, carrier gas supply system, cooling gas supply system, coolingliquid supply system, aerosol heater, and aerosol generator may becombined in any combination into the aerosol manufacture facility of thepresent invention.

EXAMPLES

The following examples are provided to aid in understanding of thepresent invention, and are not intended to in any way limit the scope ofthe present invention.

Example 1

This example demonstrates preparation of multi-phase particles of eitherneodymium titanate or barium titanate with various metals.

A titanate precursor solution is prepared for each of barium titanateand neodymium titanate. The barium titanate precursor solution isprepared by dissolving barium nitrate in water and then, with rapidstirring, adding titanium tetraisopropoxide. A fine precipitate isformed. Sufficient nitric acid is added to completely dissolve theprecipitate. Precursor solutions of various metals are prepared bydissolving the metal salt in water. The neodymium titanate precursorsolution is prepared in the same way except using neodymium nitrate.

The titanate precursor solution and the metal precursor solution aremixed in various relative quantities to obtain the desired relativequantities of titanate and metal components in the final particles. Themixed solutions are aerosolized in an ultrasonic aerosol generator withtransducers operated at 1.6 MHz and the aerosol is sent to a furnacewhere droplets in the aerosol are pyrolized to form the desiredmulti-phase particles. Air or nitrogen is used as a carrier gas, withtests involving copper and nickel also including hydrogen in an amountof 2.8 volume percent of the carrier gas.

Results are summarized in Table 2.

Example 2

A variety of materials are made, with some materials being made with andsome being made without droplet classification prior to the furnace.Various single phase and multi-phase (or composite) particles are madeas well as several coated particles. Tables 3 through 8 tabulate variousof these materials and conditions of manufacture. TABLE 2 MetalComposite Precursor(s) Temperature ° C. Carrier Gas 75/25 Pd/BaTiO₃nitrate 1000 N₂ Ag:Pd/BaTiO₃ ⁽¹⁾ nitrate 600-1100 air 75/25 Ag:Pd/BaTiO₃nitrate 1000 air 75/25 Ni/BaTiO₃ nitrate 1200 N₂ + H₂ 75/25 Ni/Nd₂TiO₇nitrate 1200 N₂ + H₂ 75/25 Cu/BaTiO₃ nitrate 1200 N₂ + H₂ 50/50Pt/BaTiO₃ chloroplatinic 1100 air acid⁽¹⁾70:30 Ag:Pd alloy, BaTiO3 varied from 5 to 90 weight percent of thecomposite.⁽²⁾30:70 Ag:Pd alloy.

TABLE 3 Phosphors Reactor Carrier Material Precursor⁽⁴⁾ Temp ° C. GasY₂O₃:Eu Yttrium nitrate, chloride or acetate and europium 500-1100 Airdopant nitrate⁽¹⁾⁽²⁾ CaTiO₃ Titanium tetraisopropoxide and calciumnitrate⁽¹⁾ 600-800  Air, N₂, O₂ CaTiO₃ “Tyzor”⁽³⁾ and calcium nitrate,titanium 600-800  Air, N₂, O₂ tetraisopropoxide and calcium nitrate⁽¹⁾CaS Calcium carbonate and thioacetic acid, various 800-1100 N₂ dopantsas metal salts⁽¹⁾ MgS Magnesium carbonate and thioacetic acid, various800-1100 N₂ dopants as metal salts⁽¹⁾ SrS Strontium carbonate andthioacetic acid, various 800-1100 N₂ dopants as metal salts⁽¹⁾ BaSBarium carbonate and thioacetic acid, various 800-1100 N₂ dopants asmetal salts⁽¹⁾ ZnS Zinc nitrate and thiourea, various dopants as metal800-950  N₂ salts⁽¹⁾ ZnS Zinc nitrate and thiourea, MnCl₂ as dopant⁽¹⁾950 N₂ Ca_(x)Sr_(1−x)S Metal carbonates or hydroxides and thioacetic800-1100 N₂ acid, various dopants as metal salts⁽¹⁾ Mg_(x)Sr_(1−x)SMetal carbonates or hydroxides and thioacetic 800-1100 N₂ acid, variousdopants as metal salts⁽¹⁾ ZnS Zn_(x)(OH)_(y)(CO₃)_(z) particles incolloidal suspension, 800-950  N₂ various dopants as metal salts,thioacetic acid ZnO:Zn⁽⁴⁾ Zinc nitrate⁽¹⁾ 700-900  N₂ + H₂ Mixture⁽¹⁾In aqueous solution⁽²⁾Urea addition improves densification of particles⁽³⁾Metal organic sold by DuPont⁽⁴⁾Some Zn reduced to Zn during manufacture, the amount of reductionbeing controllable.

TABLE 4 Pure Metals Material Precursor Temperature ° C. Carrier Gas Pdnitrate 900-1500 N₂ Ag nitrate 900-1400 air Ni nitrate 700-1400 N₂ + H₂Cu nitrate 700-1400 N₂ + H₂ Pt chloroplatinic acid 900-1500 air(H₂PtCl₆.H₂0) Au chloride 500-1100 air

TABLE 5 Metal Alloys Material Precursors Temperature ° C. Carrier Gas70/30 Pd/Ag nitrates 900-1400 N₂ 70/30 Ag/Pd nitrates 900-1500 N₂ 50/50Ni/Cu nitrates 1100 N₂ + H₂ 50/50 Cu/Ni nitrates 1200 N₂ + H₂ 70/30Cu/Zn nitrates 1000 N₂ + H₂ 90/10 Cu/Sn nitrates 1000 N₂ + H₂ 50/50Pt/Pd chloroplatinic acid 1100 N₂ palladium nitrate

TABLE 6 Coated Particles Coating Reactor Carrier Material CorePrecursor(s) Coating Precursor(s) Method Temp ° C. Gas PbO coating ironsulfate in Pb(NO₃)₂ in aqueous PVD 900 H₂ + N₂ on Fe₃O₄ core aqueoussolution solution mixture Pb coating on iron sulfate in lead nitrate inPVD 900 H₂ + N₂ Fe₃O₄ core aqueous solution aqueous solution mixture PbOcoating Ruthenium nitrosyl Pb(NO₃)₂ in aqueous PVD 1100  N₂ on RuO₂ corenitrate in aqueous solution solution SiO₂ coating Palladium nitrate inSiCl₄ CVD 1100-1300 N₂ on Pd core aqueous solution TiO₂ coatingPalladium nitrate in TiCl₄ CVD 1100-1300 N₂ on Pd core aqueous solution

TABLE 7 Composites Reactor Carrier Material Precursor(s) Temp ° C. GasPbO/Fe₃O₄ Colloidal suspension of Fe₃O₄ particles in 500-800  Airaqueous solution of Pb(NO₃)₂ Pd/SiO₂ ⁽¹⁾ 60 nm SiO₂ particles suspendedin aqueous 900-1100 N₂ solution of Pd(NO₃)₂ Pd/SiO₂ ⁽²⁾ 200 nm SiO₂particles suspended in aqueous 1100 N₂ solution of Pd(NO₃)₂ Pd/BaTiO₃Pd(NO₃)₂ Ba(NO₃)₂ and Ti(NO₃)₄ in aqueous 1100 N₂ solution Pd/TiO₂ ⁽⁴⁾Pd(NO₃)₂ and Ti(OiPr)₄ ⁽³⁾ in aqueous solution 1100 N₂ Pd/Al₂O₃ ⁽⁶⁾Pd(NO₃)₂ and Al(OsecBu)₂ ⁽⁵⁾ in aqueous solution 1100 N₂ Pd/TiO₂ ⁽⁷⁾Pd(NO₃)₂ in aqueous solution slurried with 0.25 1100 N₂ micron TiO₂particles Ag/TiO₂ ⁽⁸⁾ AgNO₃ aqueous solution with suspended 0.25  900 N₂micron TiO₂ particles Pt/TiO₂ ⁽⁹⁾ K₂PtCl₄ aqueous solution withsuspended 0.25 1100 N₂ micron TiO₂ particles Ag/TiO₂ ⁽¹⁰⁾ AgNO₃ aqueoussolution with colloidal TiO₂  900 N₂ particles Au/TiO₂ ⁽¹¹⁾ Colloidal Auand TiO₂ particles in aqueous liquid  900 N₂⁽¹⁾Morphology of particles changes from intimately mixed Pd/SiO₂ to SiO₂coating over Pd as reactor temperature is increased.⁽²⁾Coating of Pd on SiO₂ particles.⁽³⁾Titanium tetraisopropoxide.⁽⁴⁾Metal dispersed on high surface area TiO₂ support.⁽⁵⁾Al[OCH (CH₃)C₂H₅]₃.⁽⁶⁾Metal dispersed on high surface area Al₂O₃ support.⁽⁷⁾Pd coating on TiO₂ particles.⁽⁸⁾Ag coating on TiO₂ particles.⁽⁹⁾Pt coating on TiO₂ particles.⁽¹⁰⁾TiO₂ coating on Ag particles.⁽¹¹⁾TiO₂ coating on Au particles.

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations to thoseembodiments will occur to those skilled in the art. It is to beexpressly understood, however, that such modifications and adaptationsare within the scope of the present invention, as set forth in theclaims below. Further, it should be recognized that any feature of anyembodiment disclosed herein can be combined with any other feature ofany other embodiment in any combination.

1. An automated batch aerosol method for making particles of a selectedcomposition, the method comprising: batch processing of a batch ofprecursor liquid, comprising a liquid vehicle and a precursor material,to manufacture a batch of particulate product, the batch processingincluding batch initiation operations, batch termination operations andintermediate operations, the intermediate operations occurring betweenthe batch initiation operations and the batch termination operations;the intermediate operations comprising: (a) generating an aerosolstream, in an ultrasonic aerosol generator including a plurality ofactivated ultrasonic transducers, from a carrier gas and the precursorliquid, the aerosol stream including droplets comprising the precursorliquid dispersed in aerosol form in the carrier gas, the aerosolgenerator including at least one inlet receiving precursor liquid feedto the aerosol generator; (b) supplying the carrier gas to the aerosolgenerator from a carrier gas supply system in fluid communication withthe aerosol generator; (c) supplying the precursor liquid feed from aprecursor liquid supply system in fluid communication with the aerosolgenerator; and (d) forming the particles in the aerosol stream,comprising heating the aerosol stream in an aerosol heater in fluidcommunication with the aerosol generator; prior to commencement of thebatch initiation operations and after completion of the batchtermination operations, the aerosol stream not being generated; thebatch initiation operations comprising commencing generation of theaerosol stream and the batch termination operations comprising ceasinggeneration of the aerosol stream; and at least one operation during thebatch initiation operations, the intermediate operations and the batchtermination operations being automatically controlled at the directionof an electronic processor processing instructions for manufacture ofthe particles of the selected composition.
 2. The method of claim 1,wherein the batch initiation operations comprise activating theultrasonic transducers.
 3. The method of claim 2, wherein the step ofactivating the ultrasonic transducers comprises automaticallyactivating, at the direction of the electronic processor, the ultrasonictransducers.
 4. The method of claim 2, wherein a flow path for theaerosol stream comprises the aerosol generator and the aerosol heater;and the batch initiation operations comprise automatically pressuretesting the flow path for leaks prior to activating the ultrasonictransducers, the pressure testing being controlled at the direction ofthe electronic processor.
 5. The method of claim 4, wherein the flowpath further comprises an aerosol cooler downstream from the aerosolheater.
 6. The method of claim 5, wherein the flow path furthercomprises a particle collector downstream of the aerosol cooler.
 7. Themethod of claim 2, wherein the batch initiation operations comprise,prior to the step of activating the ultrasonic transducers,automatically commencing, at the direction of the electronic processor,to supply the precursor liquid feed to the aerosol generator.
 8. Themethod of claim 7, wherein the batch initiation operations comprise,after the step of commencing to supply the precursor liquid feed andprior to the step of activating the ultrasonic transducers, establishingcirculation of the precursor liquid from the precursor liquid supplysystem to the aerosol generator, through the aerosol generator and backto the precursor liquid system.
 9. The method of claim 8, wherein thestep of establishing circulation comprises automatically heating, at thedirection of the electronic processor, at least a portion of thecirculating precursor liquid, to raise the temperature of at least aportion of the aerosol generator.
 10. The method of claim 9, wherein theheating is automatically discontinued, at the direction of theelectronic processor, after the temperature of the circulating precursorliquid has risen above a predetermined level.
 11. The method of claim 2,wherein the batch initiation operations comprise, prior to the step ofactivating of the ultrasonic transducers, automatically increasing, atthe direction of the electronic processor, temperature within theaerosol heater.
 12. The method of claim 11, wherein the aerosol heatercomprises at least two end caps, a first said end cap adjacent a flowentrance into the aerosol heater and a second said end cap adjacent aflow exit from the aerosol heater, the step of increasing thetemperature within the aerosol heater comprising cooling, at thedirection of the electronic processor, at least one of the first andsecond end caps. 13-158. (Cancelled).
 159. An aerosol method for makingparticles, the method comprising: generating, in an aerosol generator,an aerosol stream comprising droplets of a precursor liquid dispersed ina carrier gas; conducting the aerosol stream from the aerosol generatorto an aerosol heater, comprising flowing the aerosol stream through aconduit located between the aerosol generator and the aerosol heater;and forming the particles in the aerosol stream, comprising heating theaerosol stream in the aerosol heater; wherein, at least a portion of theconduit is cooled during step of conducting the aerosol stream from theaerosol generator to the aerosol heater.
 160. The method of claim 159,wherein the conduit has a first conduit portion conducting flow of theaerosol stream in a first direction and a second conduit portiondirecting flow of the aerosol stream in a second direction, the firstconduit portion being upstream from the second conduit portion, the stepof cooling comprises cooling the first conduit portion.
 161. The methodof claim 160, wherein, the temperature of the aerosol stream in thefirst conduit portion is maintained a temperature low enough so that thedispersed phase in the aerosol stream flowing through the first conduitportion is maintained substantially in a droplet form; and thetemperature of the aerosol stream in the second conduit portion ismaintained at a temperature that is high enough so that at least aportion of the disperse phase in the aerosol stream in the secondconduit portion is in particulate form.
 162. The method of claim 160,wherein the first conduit portion and the second conduit portion areseparated by a bend in the conduit.
 163. The method of claim 162,wherein the bend comprises at least about a 90° change in the directionof flow from the first direction to the second direction.
 164. Themethod of claim 160, wherein the first direction is substantiallyvertical and the second direction is substantially horizontal.
 165. Themethod of claim 160, wherein the step of cooling the first conduitportion comprises directing a cooling gas at an exterior surface of thefirst conduit.
 166. The method of claim 160, wherein the second conduitportion is substantially not cooled.